[PATCH] D88782: [MemorySSA] Consistently handle lifetime.start clobbers

[Nikita Popov via Phabricator via llvm-commits]

nikic created this revision.
nikic added reviewers: asbirlea, fhahn.
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Currently lifetime.start clobbers are only considered if the UseInstruction is not a call, which doesn't really make sense to me. In particular, this means that asking for the clobber of a lifetime.start intrinsic at the memory location of that intrinsic will *not* return the intrinsic itself. (This introduces a difference between calling getClobberingMemoryAccess() without location, and calling it on the defining access with a location.)

I'm fixing this by removing the explicit lifetime.start handling from the switch -- as far as I can see, the generic code will handle this correctly already.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D88782

Files:
  llvm/lib/Analysis/MemorySSA.cpp
  llvm/unittests/Analysis/MemorySSATest.cpp


Index: llvm/unittests/Analysis/MemorySSATest.cpp
===================================================================
--- llvm/unittests/Analysis/MemorySSATest.cpp
+++ llvm/unittests/Analysis/MemorySSATest.cpp
@@ -1205,8 +1205,8 @@
   //   %bar = getelementptr i8, i8* %foo, i64 1
   //   store i8 0, i8* %foo
   //   store i8 0, i8* %bar
-  //   call void @llvm.lifetime.end.p0i8(i64 8, i32* %p)
-  //   call void @llvm.lifetime.start.p0i8(i64 8, i32* %p)
+  //   call void @llvm.lifetime.end.p0i8(i64 8, i32* %foo)
+  //   call void @llvm.lifetime.start.p0i8(i64 8, i32* %foo)
   //   store i8 0, i8* %foo
   //   store i8 0, i8* %bar
   //   ret void
@@ -1263,6 +1263,11 @@
   MemoryAccess *BarClobber =
       MSSA.getWalker()->getClobberingMemoryAccess(BarAccess);
   EXPECT_EQ(BarClobber, LifetimeStartAccess);
+
+  MemoryAccess *LifetimeStartClobber =
+      MSSA.getWalker()->getClobberingMemoryAccess(
+          LifetimeStartAccess, MemoryLocation(Foo));
+  EXPECT_EQ(LifetimeStartClobber, LifetimeStartAccess);
 }
 
 TEST_F(MemorySSATest, DefOptimizationsAreInvalidatedOnMoving) {
Index: llvm/lib/Analysis/MemorySSA.cpp
===================================================================
--- llvm/lib/Analysis/MemorySSA.cpp
+++ llvm/lib/Analysis/MemorySSA.cpp
@@ -276,11 +276,6 @@
     // clobbers where they don't really exist at all. Please see D43269 for
     // context.
     switch (II->getIntrinsicID()) {
-    case Intrinsic::lifetime_start:
-      if (UseCall)
-        return {false, NoAlias};
-      AR = AA.alias(MemoryLocation(II->getArgOperand(1)), UseLoc);
-      return {AR != NoAlias, AR};
     case Intrinsic::lifetime_end:
     case Intrinsic::invariant_start:
     case Intrinsic::invariant_end:


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