[PATCH] D98925: [BasicAA] Ignore @llvm.annotation when computing ModRefInfo.

[Clement Courbet via Phabricator via llvm-commits]

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@llvm.annotation is supposed to be ignored by code generation and
optimization:
https://llvm.org/docs/LangRef.html#llvm-annotation-intrinsic

However BasicAA considers that it may write to memory, so loads cannot
be moved across annotations.

BasicAA already ignores `llvm.assume` for this purpose. This change adds
`llvm.annotation`, `llvm.var.annotation` and `llvm.ptr.annotation`.

Fixes PR49638.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D98925

Files:
  llvm/lib/Analysis/BasicAliasAnalysis.cpp
  llvm/test/Transforms/InstCombine/annotation-intrinsic.ll


Index: llvm/test/Transforms/InstCombine/annotation-intrinsic.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/InstCombine/annotation-intrinsic.ll
@@ -0,0 +1,27 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -instcombine %s -S -o - | FileCheck %s
+
+; This tests that llvm.annotation does not prevent load combining.
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-grtev4-linux-gnu"
+
+declare i32 @llvm.annotation.i32(i32, i8*, i8*, i32) #1
+
+define dso_local i32 @annotated(i32* %c) local_unnamed_addr #0 {
+; CHECK-LABEL: @annotated(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = load i32, i32* [[C:%.*]], align 4
+; CHECK-NEXT:    [[TMP1:%.*]] = call i32 @llvm.annotation.i32(i32 [[TMP0]], i8* undef, i8* undef, i32 undef)
+; CHECK-NEXT:    [[ADD:%.*]] = add nsw i32 [[TMP1]], [[TMP0]]
+; CHECK-NEXT:    ret i32 [[ADD]]
+;
+entry:
+  %0 = load i32, i32* %c, align 4
+  %1 = call i32 @llvm.annotation.i32(i32 %0, i8* undef, i8* undef, i32 undef)
+  %2 = load i32, i32* %c, align 4
+  %add = add nsw i32 %1, %2
+  ret i32 %add
+}
+
+attributes #0 = { nofree nounwind uwtable willreturn mustprogress }
Index: llvm/lib/Analysis/BasicAliasAnalysis.cpp
===================================================================
--- llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -937,6 +937,13 @@
   // particular memory location.
   if (isIntrinsicCall(Call, Intrinsic::assume))
     return ModRefInfo::NoModRef;
+  // The same applies to annotations.
+  if (isIntrinsicCall(Call, Intrinsic::annotation))
+    return ModRefInfo::NoModRef;
+  if (isIntrinsicCall(Call, Intrinsic::var_annotation))
+    return ModRefInfo::NoModRef;
+  if (isIntrinsicCall(Call, Intrinsic::ptr_annotation))
+    return ModRefInfo::NoModRef;
 
   // Like assumes, guard intrinsics are also marked as arbitrarily writing so
   // that proper control dependencies are maintained but they never mods any


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