Support for lifetime begin/end markers in the MemorySSA use optimizer

Summary: Depends on D23072

Reviewers: george.burgess.iv

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D23076

llvm-svn: 277553

2 files changed, 68 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Utils/MemorySSA.cpp b/llvm/lib/Transforms/Utils/MemorySSA.cpp
index 58d6b04524b..8a93f4f5b16 100644
--- a/llvm/lib/Transforms/Utils/MemorySSA.cpp
+++ b/llvm/lib/Transforms/Utils/MemorySSA.cpp
@@ -192,6 +192,21 @@ struct UpwardsMemoryQuery {
   }
 };
 
+static bool lifetimeEndsAt(MemoryDef *MD, const MemoryLocation &Loc,
+                           AliasAnalysis &AA) {
+  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:
+      return false;
+    }
+  }
+  return false;
+}
+
 static bool instructionClobbersQuery(MemoryDef *MD,
                                      const MemoryLocation &UseLoc,
                                      const Instruction *UseInst,
@@ -199,6 +214,21 @@ static bool instructionClobbersQuery(MemoryDef *MD,
   Instruction *DefInst = MD->getMemoryInst();
   assert(DefInst && "Defining instruction not actually an instruction");
 
+  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:
+    case Intrinsic::lifetime_end:
+    case Intrinsic::invariant_start:
+    case Intrinsic::invariant_end:
+    case Intrinsic::assume:
+      return false;
+    default:
+      break;
+    }
+  }
+
   ImmutableCallSite UseCS(UseInst);
   if (UseCS) {
     ModRefInfo I = AA.getModRefInfo(DefInst, UseCS);
@@ -1308,7 +1338,14 @@ void MemorySSA::OptimizeUses::optimizeUsesInBlock(
       }
 
       MemoryDef *MD = cast<MemoryDef>(VersionStack[UpperBound]);
-
+      // If the lifetime of the pointer ends at this instruction, it's live on
+      // entry.
+      if (!UseMLOC.IsCall && lifetimeEndsAt(MD, UseMLOC.getLoc(), *AA)) {
+        // Reset UpperBound to liveOnEntryDef's place in the stack
+        UpperBound = 0;
+        FoundClobberResult = true;
+        break;
+      }
       if (instructionClobbersQuery(MD, MU, UseMLOC, *AA)) {
         FoundClobberResult = true;
         break;
diff --git a/llvm/test/Transforms/Util/MemorySSA/lifetime-simple.ll b/llvm/test/Transforms/Util/MemorySSA/lifetime-simple.ll
new file mode 100644
index 00000000000..cdb36e31eb9
--- /dev/null
+++ b/llvm/test/Transforms/Util/MemorySSA/lifetime-simple.ll
@@ -0,0 +1,30 @@
+; 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
+; This test checks a number of things:
+; First, the lifetime markers should not clobber any uses of Q or P.
+; Second, the loads of P are MemoryUse(LiveOnEntry) due to the placement of the markers vs the loads.
+
+define i8 @test(i8* %P, i8* %Q) {
+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-NEXT:   %0 = load i8, i8* %P
+  %0 = load i8, i8* %P
+; CHECK:  2 = MemoryDef(1)
+; CHECK-NEXT:   store i8 1, i8* %P
+  store i8 1, i8* %P
+; CHECK:  3 = MemoryDef(2)
+; CHECK-NEXT:   call void @llvm.lifetime.end(i64 32, i8* %P)
+  call void @llvm.lifetime.end(i64 32, i8* %P)
+; CHECK:  MemoryUse(liveOnEntry)
+; CHECK-NEXT:   %1 = load i8, i8* %P
+  %1 = load i8, i8* %P
+; CHECK:  MemoryUse(2)
+; CHECK-NEXT:   %2 = load i8, i8* %Q
+  %2 = load i8, i8* %Q
+  ret i8 %1
+}
+declare void @llvm.lifetime.start(i64 %S, i8* nocapture %P) readonly
+declare void @llvm.lifetime.end(i64 %S, i8* nocapture %P)