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

[Daniel Berlin via llvm-commits]

dberlin updated this revision to Diff 66519.
dberlin added a comment.

- Remove dead comment


https://reviews.llvm.org/D23076

Files:
  lib/Transforms/Utils/MemorySSA.cpp

Index: lib/Transforms/Utils/MemorySSA.cpp
===================================================================
--- lib/Transforms/Utils/MemorySSA.cpp
+++ lib/Transforms/Utils/MemorySSA.cpp
@@ -170,13 +170,40 @@
   }
 };
 
+static bool lifetimeEndsAt(MemoryDef *MD, const MemoryLocation &Loc,
+                           AliasAnalysis &AA) {
+  Instruction *Inst = MD->getMemoryInst();
+  if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
+    if (II->getIntrinsicID() == Intrinsic::lifetime_start) {
+      if (AA.isMustAlias(MemoryLocation(II->getArgOperand(1)), Loc))
+        return true;
+    }
+  }
+  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>(UseInst)) {
+    // 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);
@@ -501,7 +528,7 @@
       if (Current == StopAt)
         return {Current, false, false};
 
-      if (auto *MD = dyn_cast<MemoryDef>(Current))
+      if (auto *MD = dyn_cast<MemoryDef>(Current)) {
         if (MSSA.isLiveOnEntryDef(MD) ||
             instructionClobbersQuery(MD, Desc.Loc, Query->Inst, AA))
           return {MD, true, false};
@@ -1307,7 +1334,14 @@
       }
 
       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;


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