[llvm] r299865 - MemorySSA: Make lifetime starts defs for mustaliased pointers

[Daniel Berlin via llvm-commits]

Author: dannyb
Date: Mon Apr 10 13:46:00 2017
New Revision: 299865

URL: http://llvm.org/viewvc/llvm-project?rev=299865&view=rev
Log:
MemorySSA: Make lifetime starts defs for mustaliased pointers

Summary:
While we don't want them aliasing with other pointers, there seems to
be no point in not having them clobber must-aliased'd pointers.

If some day, we split the aliasing and ordering chains, we'd make this
not aliasing but an ordering barrier (IE it doesn't affect it's
memory, but we can't hoist it above it).

Reviewers: hfinkel, george.burgess.iv

Subscribers: Prazek, llvm-commits

Differential Revision: https://reviews.llvm.org/D31865

Modified:
    llvm/trunk/lib/Transforms/Utils/MemorySSA.cpp
    llvm/trunk/test/Transforms/Util/MemorySSA/lifetime-simple.ll

Modified: llvm/trunk/lib/Transforms/Utils/MemorySSA.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/MemorySSA.cpp?rev=299865&r1=299864&r2=299865&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/MemorySSA.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/MemorySSA.cpp Mon Apr 10 13:46:00 2017
@@ -214,12 +214,16 @@ static bool instructionClobbersQuery(Mem
                                      AliasAnalysis &AA) {
   Instruction *DefInst = MD->getMemoryInst();
   assert(DefInst && "Defining instruction not actually an instruction");
+  ImmutableCallSite UseCS(UseInst);
 
   if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(DefInst)) {
     // These intrinsics will show up as affecting memory, but they are just
     // markers.
     switch (II->getIntrinsicID()) {
     case Intrinsic::lifetime_start:
+      if (UseCS)
+        return false;
+      return AA.isMustAlias(MemoryLocation(II->getArgOperand(1)), UseLoc);
     case Intrinsic::lifetime_end:
     case Intrinsic::invariant_start:
     case Intrinsic::invariant_end:
@@ -230,7 +234,6 @@ static bool instructionClobbersQuery(Mem
     }
   }
 
-  ImmutableCallSite UseCS(UseInst);
   if (UseCS) {
     ModRefInfo I = AA.getModRefInfo(DefInst, UseCS);
     return I != MRI_NoModRef;
@@ -298,7 +301,6 @@ static bool lifetimeEndsAt(MemoryDef *MD
   Instruction *Inst = MD->getMemoryInst();
   if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
     switch (II->getIntrinsicID()) {
-    case Intrinsic::lifetime_start:
     case Intrinsic::lifetime_end:
       return AA.isMustAlias(MemoryLocation(II->getArgOperand(1)), Loc);
     default:

Modified: llvm/trunk/test/Transforms/Util/MemorySSA/lifetime-simple.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/Util/MemorySSA/lifetime-simple.ll?rev=299865&r1=299864&r2=299865&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/Util/MemorySSA/lifetime-simple.ll (original)
+++ llvm/trunk/test/Transforms/Util/MemorySSA/lifetime-simple.ll Mon Apr 10 13:46:00 2017
@@ -9,7 +9,7 @@ entry:
 ; CHECK:  1 = MemoryDef(liveOnEntry)
 ; CHECK-NEXT:   call void @llvm.lifetime.start(i64 32, i8* %P)
   call void @llvm.lifetime.start(i64 32, i8* %P)
-; CHECK:  MemoryUse(liveOnEntry)
+; CHECK:  MemoryUse(1)
 ; CHECK-NEXT:   %0 = load i8, i8* %P
   %0 = load i8, i8* %P
 ; CHECK:  2 = MemoryDef(1)