[PATCH] D31865: MemorySSA: Make lifetime starts defs for mustaliased pointers

[Daniel Berlin via Phabricator via llvm-commits]

dberlin created this revision.
Herald added a subscriber: Prazek.

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).


https://reviews.llvm.org/D31865

Files:
  lib/Transforms/Utils/MemorySSA.cpp
  test/Transforms/Util/MemorySSA/lifetime-simple.ll


Index: test/Transforms/Util/MemorySSA/lifetime-simple.ll
===================================================================
--- test/Transforms/Util/MemorySSA/lifetime-simple.ll
+++ test/Transforms/Util/MemorySSA/lifetime-simple.ll
@@ -9,7 +9,7 @@
 ; 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)
Index: lib/Transforms/Utils/MemorySSA.cpp
===================================================================
--- lib/Transforms/Utils/MemorySSA.cpp
+++ lib/Transforms/Utils/MemorySSA.cpp
@@ -220,6 +220,7 @@
     // markers.
     switch (II->getIntrinsicID()) {
     case Intrinsic::lifetime_start:
+      return AA.isMustAlias(MemoryLocation(II->getArgOperand(1)), UseLoc);
     case Intrinsic::lifetime_end:
     case Intrinsic::invariant_start:
     case Intrinsic::invariant_end:
@@ -298,7 +299,6 @@
   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:


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