[PATCH] D87149: [InstCombine] erase instructions leading up to unreachable

[Mikael Holmén via Phabricator via llvm-commits]

uabelho added a comment.

Hi!

We've run into a case where instcombine crashes with this patch:

  opt -o /dev/null bbi-47401.ll -instcombine

on

  @c = external global i16*, align 1
  
  define void @main() {
  entry:
    br label %for.cond
  
  for.cond:                                         ; preds = %g.exit, %entry
    %conv1 = phi double [ %conv, %g.exit ], [ undef, %entry ]
    br i1 undef, label %for.end, label %for.body
  
  for.body:                                         ; preds = %for.cond
    %0 = load i16*, i16** @c, align 1
    %1 = load i16, i16* %0, align 1
    %conv = sitofp i16 %1 to double
    unreachable
  
  g.exit:                                           ; No predecessors!
    br label %for.cond
  
  for.end:                                          ; preds = %for.cond
    %conv1.lcssa = phi double [ %conv1, %for.cond ]
    store double %conv1.lcssa, double* undef, align 1
    ret void
  }

results in

  opt: ../lib/Transforms/InstCombine/InstCombineInternal.h:448: virtual llvm::Instruction *llvm::InstCombinerImpl::eraseInstFromFunction(llvm::Instruction &): Assertion `I.use_empty() && "Cannot erase instruction that is used!"' failed.

I suppose it's the dead block %g.exit that messes up things.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D87149/new/

https://reviews.llvm.org/D87149