[PATCH] D132657: [DSE] Eliminate noop store even through has clobbering between LoadI and StoreI

[luxufan via Phabricator via llvm-commits]

StephenFan updated this revision to Diff 460977.
StephenFan added a comment.

No longer compare ABI alignment.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D132657/new/

https://reviews.llvm.org/D132657

Files:
  llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
  llvm/test/Transforms/DeadStoreElimination/stores-of-existing-values.ll


Index: llvm/test/Transforms/DeadStoreElimination/stores-of-existing-values.ll
===================================================================
--- llvm/test/Transforms/DeadStoreElimination/stores-of-existing-values.ll
+++ llvm/test/Transforms/DeadStoreElimination/stores-of-existing-values.ll
@@ -612,16 +612,28 @@
 ; CHECK-LABEL: @pr49927(
 ; CHECK-NEXT:    [[V:%.*]] = load i32, i32* [[P:%.*]], align 4
 ; CHECK-NEXT:    store i32 [[V]], i32* [[Q:%.*]], align 4
-; CHECK-NEXT:    store i32 [[V]], i32* [[P]], align 4
 ; CHECK-NEXT:    ret void
 ;
   %v = load i32, i32* %p, align 4
   store i32 %v, i32* %q, align 4
-  ; FIXME: this store can be eliminated
   store i32 %v, i32* %p, align 4
   ret void
 }
 
+
+define void @pr49927_unalign(i32* %q, i32* %p) {
+; CHECK-LABEL: @pr49927_unalign(
+; CHECK-NEXT:    [[V:%.*]] = load i32, i32* [[P:%.*]], align 1
+; CHECK-NEXT:    store i32 [[V]], i32* [[Q:%.*]], align 1
+; CHECK-NEXT:    store i32 [[V]], i32* [[P]], align 1
+; CHECK-NEXT:    ret void
+;
+  %v = load i32, i32* %p, align 1
+  store i32 %v, i32* %q, align 1
+  store i32 %v, i32* %p, align 1
+  ret void
+}
+
 define void @pr50339(i8* nocapture readonly %0) {
 ; CHECK-LABEL: @pr50339(
 ; CHECK-NEXT:    tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* noundef nonnull align 16 dereferenceable(16) getelementptr inbounds ([32 x i8], [32 x i8]* @a, i64 0, i64 0), i8* noundef nonnull align 1 dereferenceable(16) [[TMP0:%.*]], i64 16, i1 false)
Index: llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -1864,8 +1864,18 @@
           // We are searching for the definition of the store's destination.
           // So, if that is the same definition as the load, then this is a
           // noop. Otherwise, fail.
-          if (LoadAccess != Current)
+          if (LoadAccess != Current) {
+            if (auto *CurrentDef = dyn_cast<MemoryDef>(Current))
+              if (auto *CurrentStoreI =
+                      dyn_cast<StoreInst>(CurrentDef->getMemoryInst()))
+                if (CurrentStoreI->getOperand(0) == LoadI &&
+                    CurrentStoreI->getAlign() >=
+                        LoadI->getType()->getScalarSizeInBits() / 8)
+                  continue;
             return false;
+          }
+          // This is a potentially clobbering store, but it writes the same
+          // value, so we can safely ignore it.
         }
         return true;
       }


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