[PATCH] D23076: Support for lifetime begin/end markers in the use optimizer

[Daniel Berlin via llvm-commits]

dberlin updated this revision to Diff 66534.
dberlin added a comment.

- Reword


https://reviews.llvm.org/D23076

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

Index: test/Transforms/Util/MemorySSA/lifetime-simple.ll
===================================================================
--- /dev/null
+++ test/Transforms/Util/MemorySSA/lifetime-simple.ll
@@ -0,0 +1,23 @@
+; 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
+define i8 @test(i8* %P, i8* %Q) {
+; 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.
+entry:
+; CHECK:  1 = MemoryDef(liveOnEntry)
+  call void @llvm.lifetime.start(i64 32, i8* %P)
+; CHECK-DAG:  MemoryUse(liveOnEntry)
+  %0 = load i8, i8* %P
+; CHECK-DAG:  2 = MemoryDef(1)
+  store i8 1, i8* %P
+; CHECK-DAG:  3 = MemoryDef(2)
+  call void @llvm.lifetime.end(i64 32, i8* %P)
+; CHECK-DAG:  MemoryUse(liveOnEntry)
+  %1 = load i8, i8* %P
+; CHECK-DAG:  MemoryUse(2)
+  %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)
Index: lib/Transforms/Utils/MemorySSA.cpp
===================================================================
--- lib/Transforms/Utils/MemorySSA.cpp
+++ lib/Transforms/Utils/MemorySSA.cpp
@@ -170,13 +170,46 @@
   }
 };
 
+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:
+        {
+        if (AA.isMustAlias(MemoryLocation(II->getArgOperand(1)), Loc))
+          return true;
+        }
+    default:
+      return false;
+    }
+  }
+  return false;
+}
+
 static bool instructionClobbersQuery(MemoryDef *MD,
                                      const MemoryLocation &UseLoc,
                                      const Instruction *UseInst,
                                      AliasAnalysis &AA) {
   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);
@@ -1307,7 +1340,14 @@
       }
 
       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;


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D23076.66534.patch
Type: text/x-patch
Size: 3418 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20160802/927b33a6/attachment.bin>