LLVM: lib/Target/AArch64/AArch64CondBrTuning.cpp File Reference (original) (raw)

This file contains a pass that transforms CBZ/CBNZ/TBZ/TBNZ instructions into a conditional branch (B.cond), when the NZCV flags can be set for "free". More...

This file contains a pass that transforms CBZ/CBNZ/TBZ/TBNZ instructions into a conditional branch (B.cond), when the NZCV flags can be set for "free".

This is preferred on targets that have more flexibility when scheduling B.cond instructions as compared to CBZ/CBNZ/TBZ/TBNZ (assuming all other variables are equal). This can also reduce register pressure.

A few examples:

1. add w8, w0, w1 -> cmn w0, w1 ; CMN is an alias of ADDS. cbz w8, .LBB_2 -> b.eq .LBB0_2

2. add w8, w0, w1 -> adds w8, w0, w1 ; w8 has multiple uses. cbz w8, .LBB1_2 -> b.eq .LBB1_2

3. sub w8, w0, w1 -> subs w8, w0, w1 ; w8 has multiple uses. tbz w8, #31, .LBB6_2 -> b.pl .LBB6_2

Definition in file AArch64CondBrTuning.cpp.