[PATCH] D17128: [SimplifyCFG] Don't fold conditional branches that contain calls to convergent functions.

[Jingyue Wu via llvm-commits]

Lgtm

On Fri, Feb 12, 2016, 12:56 PM Justin Lebar <jlebar at google.com> wrote:

> jlebar updated this revision to Diff 47837.
> jlebar marked an inline comment as done.
> jlebar added a comment.
>
> Simplify test.
>
> This is a lot better, thank you for the suggestion.
>
>
> http://reviews.llvm.org/D17128
>
> Files:
>   lib/Transforms/Utils/SimplifyCFG.cpp
>   test/Transforms/SimplifyCFG/attr-convergent.ll
>
> Index: test/Transforms/SimplifyCFG/attr-convergent.ll
> ===================================================================
> --- /dev/null
> +++ test/Transforms/SimplifyCFG/attr-convergent.ll
> @@ -0,0 +1,28 @@
> +; RUN: opt < %s -simplifycfg -S | FileCheck %s
> +
> +; Checks that the SimplifyCFG pass won't duplicate a call to a function
> marked
> +; convergent.
> +;
> +; CHECK: call void @barrier
> +; CHECK-NOT: call void @barrier
> +define void @check(i1 %cond, i32* %out) {
> +entry:
> +  br i1 %cond, label %if.then, label %if.end
> +
> +if.then:
> +  store i32 5, i32* %out
> +  br label %if.end
> +
> +if.end:
> +  %x = phi i1 [ true, %entry ], [ false, %if.then ]
> +  call void @barrier()
> +  br i1 %x, label %cond.end, label %cond.false
> +
> +cond.false:
> +  br label %cond.end
> +
> +cond.end:
> +  ret void
> +}
> +
> +declare void @barrier() convergent
> Index: lib/Transforms/Utils/SimplifyCFG.cpp
> ===================================================================
> --- lib/Transforms/Utils/SimplifyCFG.cpp
> +++ lib/Transforms/Utils/SimplifyCFG.cpp
> @@ -1690,19 +1690,6 @@
>    return true;
>  }
>
> -/// \returns True if this block contains a CallInst with the NoDuplicate
> -/// attribute.
> -static bool HasNoDuplicateCall(const BasicBlock *BB) {
> -  for (BasicBlock::const_iterator I = BB->begin(), E = BB->end(); I != E;
> ++I) {
> -    const CallInst *CI = dyn_cast<CallInst>(I);
> -    if (!CI)
> -      continue;
> -    if (CI->cannotDuplicate())
> -      return true;
> -  }
> -  return false;
> -}
> -
>  /// Return true if we can thread a branch across this block.
>  static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
>    BranchInst *BI = cast<BranchInst>(BB->getTerminator());
> @@ -1747,7 +1734,12 @@
>    // Now we know that this block has multiple preds and two succs.
>    if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
>
> -  if (HasNoDuplicateCall(BB)) return false;
> +  // Can't fold blocks that contain noduplicate or convergent calls.
> +  if (llvm::any_of(*BB, [](const Instruction &I) {
> +        const CallInst *CI = dyn_cast<CallInst>(&I);
> +        return CI && (CI->cannotDuplicate() || CI->isConvergent());
> +      }))
> +    return false;
>
>    // Okay, this is a simple enough basic block.  See if any phi values are
>    // constants.
>
>
>
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