[PATCH] D31581: perform DSE through invariant.group.barrier

[Piotr Padlewski via Phabricator via llvm-commits]

Prazek created this revision.

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


https://reviews.llvm.org/D31581

Files:
  lib/Transforms/Scalar/DeadStoreElimination.cpp
  test/Transforms/DeadStoreElimination/invariant.group.barrier.ll


Index: test/Transforms/DeadStoreElimination/invariant.group.barrier.ll
===================================================================
--- /dev/null
+++ test/Transforms/DeadStoreElimination/invariant.group.barrier.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.invariant.group.barrier(i8* %ptr)
+  %ptr2 = call i8* @llvm.invariant.group.barrier(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.invariant.group.barrier(i8* %ptr)
+  %ptr2 = call i8* @llvm.invariant.group.barrier(i8* %ptr)
+; CHECK-NOT: store i8 43
+  store i8 43, i8* %ptr2
+  %ptr3 = call i8* @llvm.invariant.group.barrier(i8* %ptr2)
+  %ptr4 = call i8* @llvm.invariant.group.barrier(i8* %ptr3)
+
+; CHECK: store i8 43
+  store i8 44, i8* %ptr4
+  ret void
+}
+
+declare i8* @llvm.invariant.group.barrier(i8*)
Index: lib/Transforms/Scalar/DeadStoreElimination.cpp
===================================================================
--- lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -301,7 +301,8 @@
                                    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)
@@ -312,7 +313,7 @@
 
   // 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;
@@ -1099,7 +1100,7 @@
         int64_t InstWriteOffset, DepWriteOffset;
         OverwriteResult OR =
             isOverwrite(Loc, DepLoc, DL, *TLI, DepWriteOffset, InstWriteOffset,
-                        DepWrite, IOL);
+                        DepWrite, IOL, *AA);
         if (OR == OW_Complete) {
           DEBUG(dbgs() << "DSE: Remove Dead Store:\n  DEAD: "
                 << *DepWrite << "\n  KILLER: " << *Inst << '\n');


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D31581.93791.patch
Type: text/x-patch
Size: 2772 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20170402/3d1a1dfd/attachment.bin>