[PATCH] D19676: [MemorySSA] Special case for assume intrinsics.

[Geoff Berry via llvm-commits]

gberry created this revision.
gberry added reviewers: dberlin, george.burgess.iv.
gberry added a subscriber: llvm-commits.
Herald added a subscriber: mcrosier.

Treat assume intrinsics as not reading/writing memory despite
AA->getModRefInfo() saying they do, as is done in BasicAliasAnalysis.

http://reviews.llvm.org/D19676

Files:
  lib/Transforms/Utils/MemorySSA.cpp
  test/Transforms/Util/MemorySSA/assume.ll

Index: test/Transforms/Util/MemorySSA/assume.ll
===================================================================
--- /dev/null
+++ test/Transforms/Util/MemorySSA/assume.ll
@@ -0,0 +1,18 @@
+; RUN: opt -basicaa -print-memoryssa -verify-memoryssa -analyze < %s 2>&1 | FileCheck %s
+; RUN: opt -aa-pipeline=basic-aa -passes='print<memoryssa>' -verify-memoryssa -disable-output < %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/Transforms/Utils/MemorySSA.cpp
===================================================================
--- lib/Transforms/Utils/MemorySSA.cpp
+++ lib/Transforms/Utils/MemorySSA.cpp
@@ -364,6 +364,14 @@
   bool Def = bool(ModRef & MRI_Mod);
   bool Use = bool(ModRef & MRI_Ref);
 
+  // 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 (match(I, PatternMatch::m_Intrinsic<Intrinsic::assume>())) {
+    Def = false;
+    Use = false;
+  }
+
   // It's possible for an instruction to not modify memory at all. During
   // construction, we ignore them.
   if (IgnoreNonMemory && !Def && !Use)


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