[llvm-dev] Jump Threading duplicates dbg.declare intrinsics for fragments, bug? (original) (raw)

Mikael Holmén via llvm-dev llvm-dev at lists.llvm.org
Tue Sep 19 06:33:09 PDT 2017

Hi Björn,

I don't have any answers, just more confusion. Hopefully someone else can bring some light to this.

I'm also interested in dbg.declares and what the rules are regarding them since it's not very clear to me at the moment.

A similar fix as yours was made for duplicate non-fragment dbg.declares in r305244 and there is a bit of discussion about it in https://bugs.llvm.org//show_bug.cgi?id=33157 Maybe you've seen that?

I've run into a case where the inliner leaves two dbg.declares (with different locations since they origin from two different inlined call sites) connected to a single alloca after alloca-merging.

Then the inliner moves (what it thinks is) the one and only dbg.declare to the alloca (and thus leaves the other one in a loop). The help methods replaceDbgDeclareForAlloca()/replaceDbgDeclare()/FindAllocaDbgDeclare() all seems to think there is only one dbg.declare connected to one alloca. At least they all ignore all except the first one found.

Later loop unroll comes and unrolls the loop and then suddenly we have two absolutely identical dbg.declares and the assert in addFragmentOffset() blows. Who's at fault?

There is also an existing testcase that checks that there are indeed two dbg.declares to a single alloca: Transforms/Inline/alloca-dbgdeclare-merge.ll

Regards, Mikael

On 09/19/2017 02:27 PM, Björn Steinbrink via llvm-dev wrote:

Hi,

I'm hitting an assertion "overlapping or duplicate fragments" in the DWARF codegen in addFragmentOffset(). This originates from a duplicated dbg.declare intrinsic, declaring the same fragment twice. The duplicated call was generated by the jump threading pass. I have a patch (see below) that removes simply such duplicates, but I'm not sure whether that is the right approach. Cheers, Björn

diff --git a/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/lib/CodeGen/AsmPrinter/DwarfDebug.cpp index 499780a173b..308b6bd2b9f 100644 --- a/lib/CodeGen/AsmPrinter/DwarfDebug.cpp +++ b/lib/CodeGen/AsmPrinter/DwarfDebug.cpp @@ -220,6 +220,13 @@ ArrayRefDbgVariable::FrameIndexExpr DbgVariable::getFrameIndexExprs() const { return A.Expr->getFragmentInfo()->OffsetInBits <_ _B.Expr->getFragmentInfo()->OffsetInBits; }); + + auto last = std::unique(FrameIndexExprs.begin(), FrameIndexExprs.end(), + [](const FrameIndexExpr &A, const FrameIndexExpr &B) -> bool { + return A.FI == B.FI && A.Expr == B.Expr; + }); + FrameIndexExprs.erase(last, FrameIndexExprs.end()); + return FrameIndexExprs; }

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