How to force two virtual register allocate to the same physical register in LLVM? (original) (raw)

Problem summary

I want the FCVTZS_ZPmZ_StoS_UNDEF instruction’s 0th register and the FRINTN_ZPmZ_UNDEF_S instruction’s 0th register to be assigned the same physical Z register. I tried providing a register hint, and the allocator considered the hint but the final allocation still placed them into different physical registers.

IR Dump Before Virtual Register Rewriter

...
3600B    %56:zpr = LD1W %13:ppr_3b, %54:gpr64common, %233:gpr64common :: (dereferenceable invariant load unknown-size from %ir.uglygep, align 16, !tbaa !16)
3616B    %58:zpr = LD1W %13:ppr_3b, %57:gpr64common, %233:gpr64common :: (dereferenceable invariant load unknown-size from %ir.uglygep83, align 16, !tbaa !16)
3632B    %61:zpr = FMUL_ZZZ_S killed %56:zpr, %60:zpr
3648B    %62:zpr = FRINTN_ZPmZ_UNDEF_S undef %63:zpr, %13:ppr_3b, killed %61:zpr
3664B    %82:zpr = FCVTZS_ZPmZ_StoS_UNDEF undef %65:zpr, %13:ppr_3b, killed %62:zpr
3680B    %66:zpr = FMUL_ZZZ_S killed %58:zpr, %60:zpr
3728B    %73:zpr = COPY %82:zpr
3808B    %82:zpr = ASR_ZPmI_S %13:ppr_3b, killed %82:zpr(tied-def 0), 11
3812B    %67:zpr = FRINTN_ZPmZ_UNDEF_S undef %68:zpr, %13:ppr_3b, killed %66:zpr
3816B    %87:zpr = FCVTZS_ZPmZ_StoS_UNDEF undef %70:zpr, %13:ppr_3b, killed %67:zpr
3856B    %80:zpr = COPY %82:zpr
3860B    %74:zpr = COPY %87:zpr
...

IR Dump After Virtual Register Rewriter

...
3600B    renamable <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>z</mi><mn>16</mn><mo>=</mo><mi>L</mi><mi>D</mi><mn>1</mn><mi>W</mi><mi>r</mi><mi>e</mi><mi>n</mi><mi>a</mi><mi>m</mi><mi>a</mi><mi>b</mi><mi>l</mi><mi>e</mi></mrow><annotation encoding="application/x-tex">z16 = LD1W renamable </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6444em;"></span><span class="mord mathnormal" style="margin-right:0.04398em;">z</span><span class="mord">16</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord mathnormal">L</span><span class="mord mathnormal" style="margin-right:0.02778em;">D</span><span class="mord">1</span><span class="mord mathnormal" style="margin-right:0.13889em;">W</span><span class="mord mathnormal">re</span><span class="mord mathnormal">namab</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span></span></span></span>p0, renamable <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>x</mi><mn>9</mn><mo separator="true">,</mo><mi>r</mi><mi>e</mi><mi>n</mi><mi>a</mi><mi>m</mi><mi>a</mi><mi>b</mi><mi>l</mi><mi>e</mi></mrow><annotation encoding="application/x-tex">x9, renamable </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.8889em;vertical-align:-0.1944em;"></span><span class="mord mathnormal">x</span><span class="mord">9</span><span class="mpunct">,</span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mord mathnormal">re</span><span class="mord mathnormal">namab</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span></span></span></span>x8 :: (dereferenceable invariant load unknown-size from %ir.uglygep, align 16, !tbaa !16)
3616B    renamable <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>z</mi><mn>17</mn><mo>=</mo><mi>L</mi><mi>D</mi><mn>1</mn><mi>W</mi><mi>r</mi><mi>e</mi><mi>n</mi><mi>a</mi><mi>m</mi><mi>a</mi><mi>b</mi><mi>l</mi><mi>e</mi></mrow><annotation encoding="application/x-tex">z17 = LD1W renamable </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6444em;"></span><span class="mord mathnormal" style="margin-right:0.04398em;">z</span><span class="mord">17</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord mathnormal">L</span><span class="mord mathnormal" style="margin-right:0.02778em;">D</span><span class="mord">1</span><span class="mord mathnormal" style="margin-right:0.13889em;">W</span><span class="mord mathnormal">re</span><span class="mord mathnormal">namab</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span></span></span></span>p0, renamable <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>x</mi><mn>10</mn><mo separator="true">,</mo><mi>r</mi><mi>e</mi><mi>n</mi><mi>a</mi><mi>m</mi><mi>a</mi><mi>b</mi><mi>l</mi><mi>e</mi></mrow><annotation encoding="application/x-tex">x10, renamable </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.8889em;vertical-align:-0.1944em;"></span><span class="mord mathnormal">x</span><span class="mord">10</span><span class="mpunct">,</span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mord mathnormal">re</span><span class="mord mathnormal">namab</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span></span></span></span>x8 :: (dereferenceable invariant load unknown-size from %ir.uglygep83, align 16, !tbaa !16)
3632B    renamable <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>z</mi><mn>16</mn><mo>=</mo><mi>F</mi><mi>M</mi><mi>U</mi><msub><mi>L</mi><mi>Z</mi></msub><mi>Z</mi><msub><mi>Z</mi><mi>S</mi></msub><mi>k</mi><mi>i</mi><mi>l</mi><mi>l</mi><mi>e</mi><mi>d</mi><mi>r</mi><mi>e</mi><mi>n</mi><mi>a</mi><mi>m</mi><mi>a</mi><mi>b</mi><mi>l</mi><mi>e</mi></mrow><annotation encoding="application/x-tex">z16 = FMUL_ZZZ_S killed renamable </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6444em;"></span><span class="mord mathnormal" style="margin-right:0.04398em;">z</span><span class="mord">16</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.8444em;vertical-align:-0.15em;"></span><span class="mord mathnormal" style="margin-right:0.10903em;">FM</span><span class="mord mathnormal" style="margin-right:0.10903em;">U</span><span class="mord"><span class="mord mathnormal">L</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3283em;"><span style="top:-2.55em;margin-left:0em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight" style="margin-right:0.07153em;">Z</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mord mathnormal" style="margin-right:0.07153em;">Z</span><span class="mord"><span class="mord mathnormal" style="margin-right:0.07153em;">Z</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3283em;"><span style="top:-2.55em;margin-left:-0.0715em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight" style="margin-right:0.05764em;">S</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mord mathnormal">ki</span><span class="mord mathnormal" style="margin-right:0.01968em;">ll</span><span class="mord mathnormal">e</span><span class="mord mathnormal">d</span><span class="mord mathnormal">re</span><span class="mord mathnormal">namab</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span></span></span></span>z16, renamable $z0
3648B    renamable <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>z</mi><mn>16</mn><mo>=</mo><mi>F</mi><mi>R</mi><mi>I</mi><mi>N</mi><mi>T</mi><msub><mi>N</mi><mi>Z</mi></msub><mi>P</mi><mi>m</mi><msub><mi>Z</mi><mi>U</mi></msub><mi>N</mi><mi>D</mi><mi>E</mi><msub><mi>F</mi><mi>S</mi></msub><mi>u</mi><mi>n</mi><mi>d</mi><mi>e</mi><mi>f</mi><mi>r</mi><mi>e</mi><mi>n</mi><mi>a</mi><mi>m</mi><mi>a</mi><mi>b</mi><mi>l</mi><mi>e</mi></mrow><annotation encoding="application/x-tex">z16 = FRINTN_ZPmZ_UNDEF_S undef renamable </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6444em;"></span><span class="mord mathnormal" style="margin-right:0.04398em;">z</span><span class="mord">16</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.8889em;vertical-align:-0.1944em;"></span><span class="mord mathnormal" style="margin-right:0.00773em;">FR</span><span class="mord mathnormal" style="margin-right:0.07847em;">I</span><span class="mord mathnormal" style="margin-right:0.13889em;">NT</span><span class="mord"><span class="mord mathnormal" style="margin-right:0.10903em;">N</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3283em;"><span style="top:-2.55em;margin-left:-0.109em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight" style="margin-right:0.07153em;">Z</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mord mathnormal" style="margin-right:0.13889em;">P</span><span class="mord mathnormal">m</span><span class="mord"><span class="mord mathnormal" style="margin-right:0.07153em;">Z</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3283em;"><span style="top:-2.55em;margin-left:-0.0715em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight" style="margin-right:0.10903em;">U</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mord mathnormal" style="margin-right:0.10903em;">N</span><span class="mord mathnormal" style="margin-right:0.02778em;">D</span><span class="mord mathnormal" style="margin-right:0.05764em;">E</span><span class="mord"><span class="mord mathnormal" style="margin-right:0.13889em;">F</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3283em;"><span style="top:-2.55em;margin-left:-0.1389em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight" style="margin-right:0.05764em;">S</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mord mathnormal">u</span><span class="mord mathnormal">n</span><span class="mord mathnormal">d</span><span class="mord mathnormal">e</span><span class="mord mathnormal" style="margin-right:0.10764em;">f</span><span class="mord mathnormal">re</span><span class="mord mathnormal">namab</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span></span></span></span>z0, renamable <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>p</mi><mn>0</mn><mo separator="true">,</mo><mi>k</mi><mi>i</mi><mi>l</mi><mi>l</mi><mi>e</mi><mi>d</mi><mi>r</mi><mi>e</mi><mi>n</mi><mi>a</mi><mi>m</mi><mi>a</mi><mi>b</mi><mi>l</mi><mi>e</mi></mrow><annotation encoding="application/x-tex">p0, killed renamable </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.8889em;vertical-align:-0.1944em;"></span><span class="mord mathnormal">p</span><span class="mord">0</span><span class="mpunct">,</span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mord mathnormal">ki</span><span class="mord mathnormal" style="margin-right:0.01968em;">ll</span><span class="mord mathnormal">e</span><span class="mord mathnormal">d</span><span class="mord mathnormal">re</span><span class="mord mathnormal">namab</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span></span></span></span>z16
3664B    renamable <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>z</mi><mn>19</mn><mo>=</mo><mi>F</mi><mi>C</mi><mi>V</mi><mi>T</mi><mi>Z</mi><msub><mi>S</mi><mi>Z</mi></msub><mi>P</mi><mi>m</mi><msub><mi>Z</mi><mi>S</mi></msub><mi>t</mi><mi>o</mi><msub><mi>S</mi><mi>U</mi></msub><mi>N</mi><mi>D</mi><mi>E</mi><mi>F</mi><mi>u</mi><mi>n</mi><mi>d</mi><mi>e</mi><mi>f</mi><mi>r</mi><mi>e</mi><mi>n</mi><mi>a</mi><mi>m</mi><mi>a</mi><mi>b</mi><mi>l</mi><mi>e</mi></mrow><annotation encoding="application/x-tex">z19 = FCVTZS_ZPmZ_StoS_UNDEF undef renamable </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6444em;"></span><span class="mord mathnormal" style="margin-right:0.04398em;">z</span><span class="mord">19</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.8889em;vertical-align:-0.1944em;"></span><span class="mord mathnormal" style="margin-right:0.07153em;">FC</span><span class="mord mathnormal" style="margin-right:0.22222em;">V</span><span class="mord mathnormal" style="margin-right:0.07153em;">TZ</span><span class="mord"><span class="mord mathnormal" style="margin-right:0.05764em;">S</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3283em;"><span style="top:-2.55em;margin-left:-0.0576em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight" style="margin-right:0.07153em;">Z</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mord mathnormal" style="margin-right:0.13889em;">P</span><span class="mord mathnormal">m</span><span class="mord"><span class="mord mathnormal" style="margin-right:0.07153em;">Z</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3283em;"><span style="top:-2.55em;margin-left:-0.0715em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight" style="margin-right:0.05764em;">S</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mord mathnormal">t</span><span class="mord mathnormal">o</span><span class="mord"><span class="mord mathnormal" style="margin-right:0.05764em;">S</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3283em;"><span style="top:-2.55em;margin-left:-0.0576em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight" style="margin-right:0.10903em;">U</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mord mathnormal" style="margin-right:0.10903em;">N</span><span class="mord mathnormal" style="margin-right:0.02778em;">D</span><span class="mord mathnormal" style="margin-right:0.13889em;">EF</span><span class="mord mathnormal">u</span><span class="mord mathnormal">n</span><span class="mord mathnormal">d</span><span class="mord mathnormal">e</span><span class="mord mathnormal" style="margin-right:0.10764em;">f</span><span class="mord mathnormal">re</span><span class="mord mathnormal">namab</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span></span></span></span>z0, renamable <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>p</mi><mn>0</mn><mo separator="true">,</mo><mi>k</mi><mi>i</mi><mi>l</mi><mi>l</mi><mi>e</mi><mi>d</mi><mi>r</mi><mi>e</mi><mi>n</mi><mi>a</mi><mi>m</mi><mi>a</mi><mi>b</mi><mi>l</mi><mi>e</mi></mrow><annotation encoding="application/x-tex">p0, killed renamable </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.8889em;vertical-align:-0.1944em;"></span><span class="mord mathnormal">p</span><span class="mord">0</span><span class="mpunct">,</span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mord mathnormal">ki</span><span class="mord mathnormal" style="margin-right:0.01968em;">ll</span><span class="mord mathnormal">e</span><span class="mord mathnormal">d</span><span class="mord mathnormal">re</span><span class="mord mathnormal">namab</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span></span></span></span>z16
3680B    renamable <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>z</mi><mn>17</mn><mo>=</mo><mi>F</mi><mi>M</mi><mi>U</mi><msub><mi>L</mi><mi>Z</mi></msub><mi>Z</mi><msub><mi>Z</mi><mi>S</mi></msub><mi>k</mi><mi>i</mi><mi>l</mi><mi>l</mi><mi>e</mi><mi>d</mi><mi>r</mi><mi>e</mi><mi>n</mi><mi>a</mi><mi>m</mi><mi>a</mi><mi>b</mi><mi>l</mi><mi>e</mi></mrow><annotation encoding="application/x-tex">z17 = FMUL_ZZZ_S killed renamable </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6444em;"></span><span class="mord mathnormal" style="margin-right:0.04398em;">z</span><span class="mord">17</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.8444em;vertical-align:-0.15em;"></span><span class="mord mathnormal" style="margin-right:0.10903em;">FM</span><span class="mord mathnormal" style="margin-right:0.10903em;">U</span><span class="mord"><span class="mord mathnormal">L</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3283em;"><span style="top:-2.55em;margin-left:0em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight" style="margin-right:0.07153em;">Z</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mord mathnormal" style="margin-right:0.07153em;">Z</span><span class="mord"><span class="mord mathnormal" style="margin-right:0.07153em;">Z</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3283em;"><span style="top:-2.55em;margin-left:-0.0715em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight" style="margin-right:0.05764em;">S</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mord mathnormal">ki</span><span class="mord mathnormal" style="margin-right:0.01968em;">ll</span><span class="mord mathnormal">e</span><span class="mord mathnormal">d</span><span class="mord mathnormal">re</span><span class="mord mathnormal">namab</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span></span></span></span>z17, renamable $z0
3728B    renamable <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>z</mi><mn>16</mn><mo>=</mo><mi>C</mi><mi>O</mi><mi>P</mi><mi>Y</mi><mi>r</mi><mi>e</mi><mi>n</mi><mi>a</mi><mi>m</mi><mi>a</mi><mi>b</mi><mi>l</mi><mi>e</mi></mrow><annotation encoding="application/x-tex">z16 = COPY renamable </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6444em;"></span><span class="mord mathnormal" style="margin-right:0.04398em;">z</span><span class="mord">16</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord mathnormal" style="margin-right:0.13889em;">COP</span><span class="mord mathnormal" style="margin-right:0.22222em;">Y</span><span class="mord mathnormal">re</span><span class="mord mathnormal">namab</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span></span></span></span>z19
3808B    renamable <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>z</mi><mn>19</mn><mo>=</mo><mi>A</mi><mi>S</mi><msub><mi>R</mi><mi>Z</mi></msub><mi>P</mi><mi>m</mi><msub><mi>I</mi><mi>S</mi></msub><mi>r</mi><mi>e</mi><mi>n</mi><mi>a</mi><mi>m</mi><mi>a</mi><mi>b</mi><mi>l</mi><mi>e</mi></mrow><annotation encoding="application/x-tex">z19 = ASR_ZPmI_S renamable </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6444em;"></span><span class="mord mathnormal" style="margin-right:0.04398em;">z</span><span class="mord">19</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.8444em;vertical-align:-0.15em;"></span><span class="mord mathnormal">A</span><span class="mord mathnormal" style="margin-right:0.05764em;">S</span><span class="mord"><span class="mord mathnormal" style="margin-right:0.00773em;">R</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3283em;"><span style="top:-2.55em;margin-left:-0.0077em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight" style="margin-right:0.07153em;">Z</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mord mathnormal" style="margin-right:0.13889em;">P</span><span class="mord mathnormal">m</span><span class="mord"><span class="mord mathnormal" style="margin-right:0.07847em;">I</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3283em;"><span style="top:-2.55em;margin-left:-0.0785em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight" style="margin-right:0.05764em;">S</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mord mathnormal">re</span><span class="mord mathnormal">namab</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span></span></span></span>p0, killed renamable $z19(tied-def 0), 11
3812B    renamable <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>z</mi><mn>17</mn><mo>=</mo><mi>F</mi><mi>R</mi><mi>I</mi><mi>N</mi><mi>T</mi><msub><mi>N</mi><mi>Z</mi></msub><mi>P</mi><mi>m</mi><msub><mi>Z</mi><mi>U</mi></msub><mi>N</mi><mi>D</mi><mi>E</mi><msub><mi>F</mi><mi>S</mi></msub><mi>u</mi><mi>n</mi><mi>d</mi><mi>e</mi><mi>f</mi><mi>r</mi><mi>e</mi><mi>n</mi><mi>a</mi><mi>m</mi><mi>a</mi><mi>b</mi><mi>l</mi><mi>e</mi></mrow><annotation encoding="application/x-tex">z17 = FRINTN_ZPmZ_UNDEF_S undef renamable </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6444em;"></span><span class="mord mathnormal" style="margin-right:0.04398em;">z</span><span class="mord">17</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.8889em;vertical-align:-0.1944em;"></span><span class="mord mathnormal" style="margin-right:0.00773em;">FR</span><span class="mord mathnormal" style="margin-right:0.07847em;">I</span><span class="mord mathnormal" style="margin-right:0.13889em;">NT</span><span class="mord"><span class="mord mathnormal" style="margin-right:0.10903em;">N</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3283em;"><span style="top:-2.55em;margin-left:-0.109em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight" style="margin-right:0.07153em;">Z</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mord mathnormal" style="margin-right:0.13889em;">P</span><span class="mord mathnormal">m</span><span class="mord"><span class="mord mathnormal" style="margin-right:0.07153em;">Z</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3283em;"><span style="top:-2.55em;margin-left:-0.0715em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight" style="margin-right:0.10903em;">U</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mord mathnormal" style="margin-right:0.10903em;">N</span><span class="mord mathnormal" style="margin-right:0.02778em;">D</span><span class="mord mathnormal" style="margin-right:0.05764em;">E</span><span class="mord"><span class="mord mathnormal" style="margin-right:0.13889em;">F</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3283em;"><span style="top:-2.55em;margin-left:-0.1389em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight" style="margin-right:0.05764em;">S</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mord mathnormal">u</span><span class="mord mathnormal">n</span><span class="mord mathnormal">d</span><span class="mord mathnormal">e</span><span class="mord mathnormal" style="margin-right:0.10764em;">f</span><span class="mord mathnormal">re</span><span class="mord mathnormal">namab</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span></span></span></span>z0, renamable <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>p</mi><mn>0</mn><mo separator="true">,</mo><mi>k</mi><mi>i</mi><mi>l</mi><mi>l</mi><mi>e</mi><mi>d</mi><mi>r</mi><mi>e</mi><mi>n</mi><mi>a</mi><mi>m</mi><mi>a</mi><mi>b</mi><mi>l</mi><mi>e</mi></mrow><annotation encoding="application/x-tex">p0, killed renamable </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.8889em;vertical-align:-0.1944em;"></span><span class="mord mathnormal">p</span><span class="mord">0</span><span class="mpunct">,</span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mord mathnormal">ki</span><span class="mord mathnormal" style="margin-right:0.01968em;">ll</span><span class="mord mathnormal">e</span><span class="mord mathnormal">d</span><span class="mord mathnormal">re</span><span class="mord mathnormal">namab</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span></span></span></span>z17
3816B    renamable <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>z</mi><mn>18</mn><mo>=</mo><mi>F</mi><mi>C</mi><mi>V</mi><mi>T</mi><mi>Z</mi><msub><mi>S</mi><mi>Z</mi></msub><mi>P</mi><mi>m</mi><msub><mi>Z</mi><mi>S</mi></msub><mi>t</mi><mi>o</mi><msub><mi>S</mi><mi>U</mi></msub><mi>N</mi><mi>D</mi><mi>E</mi><mi>F</mi><mi>u</mi><mi>n</mi><mi>d</mi><mi>e</mi><mi>f</mi><mi>r</mi><mi>e</mi><mi>n</mi><mi>a</mi><mi>m</mi><mi>a</mi><mi>b</mi><mi>l</mi><mi>e</mi></mrow><annotation encoding="application/x-tex">z18 = FCVTZS_ZPmZ_StoS_UNDEF undef renamable </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6444em;"></span><span class="mord mathnormal" style="margin-right:0.04398em;">z</span><span class="mord">18</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.8889em;vertical-align:-0.1944em;"></span><span class="mord mathnormal" style="margin-right:0.07153em;">FC</span><span class="mord mathnormal" style="margin-right:0.22222em;">V</span><span class="mord mathnormal" style="margin-right:0.07153em;">TZ</span><span class="mord"><span class="mord mathnormal" style="margin-right:0.05764em;">S</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3283em;"><span style="top:-2.55em;margin-left:-0.0576em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight" style="margin-right:0.07153em;">Z</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mord mathnormal" style="margin-right:0.13889em;">P</span><span class="mord mathnormal">m</span><span class="mord"><span class="mord mathnormal" style="margin-right:0.07153em;">Z</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3283em;"><span style="top:-2.55em;margin-left:-0.0715em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight" style="margin-right:0.05764em;">S</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mord mathnormal">t</span><span class="mord mathnormal">o</span><span class="mord"><span class="mord mathnormal" style="margin-right:0.05764em;">S</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3283em;"><span style="top:-2.55em;margin-left:-0.0576em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight" style="margin-right:0.10903em;">U</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mord mathnormal" style="margin-right:0.10903em;">N</span><span class="mord mathnormal" style="margin-right:0.02778em;">D</span><span class="mord mathnormal" style="margin-right:0.13889em;">EF</span><span class="mord mathnormal">u</span><span class="mord mathnormal">n</span><span class="mord mathnormal">d</span><span class="mord mathnormal">e</span><span class="mord mathnormal" style="margin-right:0.10764em;">f</span><span class="mord mathnormal">re</span><span class="mord mathnormal">namab</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span></span></span></span>z0, renamable <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>p</mi><mn>0</mn><mo separator="true">,</mo><mi>k</mi><mi>i</mi><mi>l</mi><mi>l</mi><mi>e</mi><mi>d</mi><mi>r</mi><mi>e</mi><mi>n</mi><mi>a</mi><mi>m</mi><mi>a</mi><mi>b</mi><mi>l</mi><mi>e</mi></mrow><annotation encoding="application/x-tex">p0, killed renamable </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.8889em;vertical-align:-0.1944em;"></span><span class="mord mathnormal">p</span><span class="mord">0</span><span class="mpunct">,</span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mord mathnormal">ki</span><span class="mord mathnormal" style="margin-right:0.01968em;">ll</span><span class="mord mathnormal">e</span><span class="mord mathnormal">d</span><span class="mord mathnormal">re</span><span class="mord mathnormal">namab</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span></span></span></span>z17
3856B    renamable <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>z</mi><mn>20</mn><mo>=</mo><mi>C</mi><mi>O</mi><mi>P</mi><mi>Y</mi><mi>r</mi><mi>e</mi><mi>n</mi><mi>a</mi><mi>m</mi><mi>a</mi><mi>b</mi><mi>l</mi><mi>e</mi></mrow><annotation encoding="application/x-tex">z20 = COPY renamable </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6444em;"></span><span class="mord mathnormal" style="margin-right:0.04398em;">z</span><span class="mord">20</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord mathnormal" style="margin-right:0.13889em;">COP</span><span class="mord mathnormal" style="margin-right:0.22222em;">Y</span><span class="mord mathnormal">re</span><span class="mord mathnormal">namab</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span></span></span></span>z19
3860B    renamable <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>z</mi><mn>17</mn><mo>=</mo><mi>C</mi><mi>O</mi><mi>P</mi><mi>Y</mi><mi>r</mi><mi>e</mi><mi>n</mi><mi>a</mi><mi>m</mi><mi>a</mi><mi>b</mi><mi>l</mi><mi>e</mi></mrow><annotation encoding="application/x-tex">z17 = COPY renamable </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6444em;"></span><span class="mord mathnormal" style="margin-right:0.04398em;">z</span><span class="mord">17</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord mathnormal" style="margin-right:0.13889em;">COP</span><span class="mord mathnormal" style="margin-right:0.22222em;">Y</span><span class="mord mathnormal">re</span><span class="mord mathnormal">namab</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span></span></span></span>z18
...

Allocator debug excerpts showing hints were present but ignored

...
selectOrSplit ZPR:%62 [3648r,3664r:0) 0@3648r  weight:INF w=INF
assigning %62 to $z16: B16 [3648r,3664r:0) 0@3648r Z16_HI [3648r,3664r:0) 0@3648r

selectOrSplit ZPR:%82 [3664r,3808r:2)[3808r,3936r:0)[3936r,4020r:1)[4020r,4032r:3)[4032r,4344r:4)[4344r,4464r:5)[4464r,4512r:6) 0@3808r 1@3936r 2@3664r 3@4020r 4@4032r 5@4344r 6@4464r  weight:2.977558e-01 w=2.977558e-01
hints: $z16
assigning %82 to $z19: B19 [3664r,3808r:2)[3808r,3936r:0)[3936r,4020r:1)[4020r,4032r:3)[4032r,4344r:4)[4344r,4464r:5)[4464r,4512r:6) 0@3808r 1@3936r 2@3664r 3@4020r 4@4032r 5@4344r 6@4464r Z19_HI [3664r,3808r:2)[3808r,3936r:0)[3936r,4020r:1)[4020r,4032r:3)[4032r,4344r:4)[4344r,4464r:5)[4464r,4512r:6) 0@3808r 1@3936r 2@3664r 3@4020r 4@4032r 5@4344r 6@4464r
...

What I tried

Added a register hint (to prefer $z16 for %82) — allocator logged the hint but still assigned %82 to $z19.

Desired outcome

Force/ensure that the 0th register of FCVTZS_ZPmZ_StoS_UNDEF and the 0th register of FRINTN_ZPmZ_UNDEF_S are assigned the same physical Z register.

Questions / request for help

Is there a reliable way to force two virtual ZPR register values to be assigned the same physical Z register in LLVM’s register allocator for SVE targets? Are there known allocator limitations or interactions that prevent the allocator from honoring such hints in this pattern?

Thanks in advance for any suggestions or pointers!