[PATCH] D87386: [DSE,MemorySSA] Handle atomic stores expliclty in isReadClobber.

[Florian Hahn via Phabricator via llvm-commits]

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rG9969c317ff08: [DSE,MemorySSA] Handle atomic stores explicitly in isReadClobber. (authored by fhahn).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D87386/new/

https://reviews.llvm.org/D87386

Files:
  llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
  llvm/test/Transforms/DeadStoreElimination/MSSA/atomic-todo.ll
  llvm/test/Transforms/DeadStoreElimination/MSSA/atomic.ll


Index: llvm/test/Transforms/DeadStoreElimination/MSSA/atomic.ll
===================================================================
--- llvm/test/Transforms/DeadStoreElimination/MSSA/atomic.ll
+++ llvm/test/Transforms/DeadStoreElimination/MSSA/atomic.ll
@@ -88,6 +88,17 @@
   ret i32 %x
 }
 
+; DSE across monotonic store (allowed as long as the eliminated store isUnordered)
+define void @test10() {
+; CHECK-LABEL: test10
+; CHECK-NOT: store i32 0
+; CHECK: store i32 1
+  store i32 0, i32* @x
+  store atomic i32 42, i32* @y monotonic, align 4
+  store i32 1, i32* @x
+  ret void
+}
+
 ; DSE across monotonic load (forbidden since the eliminated store is atomic)
 define i32 @test11() {
 ; CHECK-LABEL: @test11(
Index: llvm/test/Transforms/DeadStoreElimination/MSSA/atomic-todo.ll
===================================================================
--- llvm/test/Transforms/DeadStoreElimination/MSSA/atomic-todo.ll
+++ llvm/test/Transforms/DeadStoreElimination/MSSA/atomic-todo.ll
@@ -21,14 +21,3 @@
   store i32 1, i32* @x
   ret i32 %x
 }
-
-; DSE across monotonic store (allowed as long as the eliminated store isUnordered)
-define void @test10() {
-; CHECK-LABEL: test10
-; CHECK-NOT: store i32 0
-; CHECK: store i32 1
-  store i32 0, i32* @x
-  store atomic i32 42, i32* @y monotonic, align 4
-  store i32 1, i32* @x
-  ret void
-}
Index: llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -1824,6 +1824,11 @@
 
   // Returns true if \p Use may read from \p DefLoc.
   bool isReadClobber(MemoryLocation DefLoc, Instruction *UseInst) {
+    // Monotonic or weaker atomic stores can be re-ordered and do not need to be
+    // treated as read clobber.
+    if (auto SI = dyn_cast<StoreInst>(UseInst))
+      return isStrongerThan(SI->getOrdering(), AtomicOrdering::Monotonic);
+
     if (!UseInst->mayReadFromMemory())
       return false;
 


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