perform DSE through launder.invariant.group

Summary:
Alias Analysis knows that llvm.launder.invariant.group
returns pointer that mustalias argument, but this information
wasn't used, therefor we didn't DSE through launder.invariant.group

Reviewers: chandlerc, dberlin, bogner, hfinkel, efriedma

Reviewed By: dberlin

Subscribers: amharc, llvm-commits, nlewycky, rsmith

Differential Revision: https://reviews.llvm.org/D31581

llvm-svn: 331449

diff --git a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
index b3dbe4d..201d0f0 100644 (file)
--- a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -343,7 +343,8 @@ static OverwriteResult isOverwrite(const MemoryLocation &Later,
                                    const TargetLibraryInfo &TLI,
                                    int64_t &EarlierOff, int64_t &LaterOff,
                                    Instruction *DepWrite,
-                                   InstOverlapIntervalsTy &IOL) {
+                                   InstOverlapIntervalsTy &IOL,
+                                   AliasAnalysis &AA) {
   // If we don't know the sizes of either access, then we can't do a comparison.
   if (Later.Size == MemoryLocation::UnknownSize ||
       Earlier.Size == MemoryLocation::UnknownSize)
@@ -354,7 +355,7 @@ static OverwriteResult isOverwrite(const MemoryLocation &Later,
 
   // If the start pointers are the same, we just have to compare sizes to see if
   // the later store was larger than the earlier store.
-  if (P1 == P2) {
+  if (P1 == P2 || AA.isMustAlias(P1, P2)) {
     // Make sure that the Later size is >= the Earlier size.
     if (Later.Size >= Earlier.Size)
       return OW_Complete;
@@ -1162,9 +1163,8 @@ static bool eliminateDeadStores(BasicBlock &BB, AliasAnalysis *AA,
       if (isRemovable(DepWrite) &&
           !isPossibleSelfRead(Inst, Loc, DepWrite, *TLI, *AA)) {
         int64_t InstWriteOffset, DepWriteOffset;
-        OverwriteResult OR =
-            isOverwrite(Loc, DepLoc, DL, *TLI, DepWriteOffset, InstWriteOffset,
-                        DepWrite, IOL);
+        OverwriteResult OR = isOverwrite(Loc, DepLoc, DL, *TLI, DepWriteOffset,
+                                         InstWriteOffset, DepWrite, IOL, *AA);
         if (OR == OW_Complete) {
           DEBUG(dbgs() << "DSE: Remove Dead Store:\n  DEAD: "
                 << *DepWrite << "\n  KILLER: " << *Inst << '\n');

diff --git a/llvm/test/Transforms/DeadStoreElimination/launder.invariant.group.ll b/llvm/test/Transforms/DeadStoreElimination/launder.invariant.group.ll
new file mode 100644 (file)
index 0000000..dfa316e
--- /dev/null
+++ b/llvm/test/Transforms/DeadStoreElimination/launder.invariant.group.ll
@@ -0,0 +1,30 @@
+; RUN: opt < %s -basicaa -dse -S | FileCheck %s
+
+; CHECK-LABEL: void @skipBarrier(i8* %ptr)
+define void @skipBarrier(i8* %ptr) {
+; CHECK-NOT: store i8 42
+  store i8 42, i8* %ptr
+; CHECK: %ptr2 = call i8* @llvm.launder.invariant.group.p0i8(i8* %ptr)
+  %ptr2 = call i8* @llvm.launder.invariant.group.p0i8(i8* %ptr)
+; CHECK: store i8 43
+  store i8 43, i8* %ptr2
+  ret void
+}
+
+; CHECK-LABEL: void @skip2Barriers(i8* %ptr)
+define void @skip2Barriers(i8* %ptr) {
+; CHECK-NOT: store i8 42
+  store i8 42, i8* %ptr
+; CHECK: %ptr2 = call i8* @llvm.launder.invariant.group.p0i8(i8* %ptr)
+  %ptr2 = call i8* @llvm.launder.invariant.group.p0i8(i8* %ptr)
+; CHECK-NOT: store i8 43
+  store i8 43, i8* %ptr2
+  %ptr3 = call i8* @llvm.launder.invariant.group.p0i8(i8* %ptr2)
+  %ptr4 = call i8* @llvm.launder.invariant.group.p0i8(i8* %ptr3)
+
+; CHECK: store i8 44
+  store i8 44, i8* %ptr4
+  ret void
+}
+
+declare i8* @llvm.launder.invariant.group.p0i8(i8*)