[PATCH] D19730: [BasicAA] Treat llvm.assume as not accessing memory in getModRefBehavior(Function)

[Daniel Berlin via llvm-commits]

LGTM

On Fri, Apr 29, 2016 at 10:15 AM, Geoff Berry <gberry at codeaurora.org> wrote:

> gberry created this revision.
> gberry added reviewers: dberlin, chandlerc, hfinkel, reames, sanjoy.
> gberry added a subscriber: llvm-commits.
> Herald added a subscriber: mcrosier.
>
> http://reviews.llvm.org/D19730
>
> Files:
>   lib/Analysis/BasicAliasAnalysis.cpp
>   test/Transforms/Util/MemorySSA/assume.ll
>
> Index: test/Transforms/Util/MemorySSA/assume.ll
> ===================================================================
> --- /dev/null
> +++ test/Transforms/Util/MemorySSA/assume.ll
> @@ -0,0 +1,17 @@
> +; RUN: opt -basicaa -print-memoryssa -verify-memoryssa -analyze < %s 2>&1
> | FileCheck %s
> +;
> +; Ensures that assumes are treated as not reading or writing memory.
> +
> +declare void @llvm.assume(i1)
> +
> +define i32 @foo(i32* %a, i32* %b, i1 %c) {
> +; CHECK: 1 = MemoryDef(liveOnEntry)
> +; CHECK-NEXT: store i32 4
> +  store i32 4, i32* %a, align 4
> +; CHECK: call void @llvm.assume
> +  call void @llvm.assume(i1 %c)
> +; CHECK: MemoryUse(1)
> +; CHECK-NEXT: %1 = load i32
> +  %1 = load i32, i32* %a, align 4
> +  ret i32 %1
> +}
> Index: lib/Analysis/BasicAliasAnalysis.cpp
> ===================================================================
> --- lib/Analysis/BasicAliasAnalysis.cpp
> +++ lib/Analysis/BasicAliasAnalysis.cpp
> @@ -575,6 +575,12 @@
>    if (F->doesNotAccessMemory())
>      return FMRB_DoesNotAccessMemory;
>
> +  // While the assume intrinsic is marked as arbitrarily writing so that
> +  // proper control dependencies will be maintained, it never aliases any
> +  // particular memory location.
> +  if (F->getIntrinsicID() == Intrinsic::assume)
> +    return FMRB_DoesNotAccessMemory;
> +
>    FunctionModRefBehavior Min = FMRB_UnknownModRefBehavior;
>
>    // If the function declares it only reads memory, go with that.
>
>
>
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