[PATCH] D126486: [LoopIdiom] Fix bailout for aliasing in memcpy transform.

[Eli Friedman 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 rGabdf0da8009f: [LoopIdiom] Fix bailout for aliasing in memcpy transform. (authored by efriedma).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D126486/new/

https://reviews.llvm.org/D126486

Files:
  llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
  llvm/test/Transforms/LoopIdiom/basic.ll


Index: llvm/test/Transforms/LoopIdiom/basic.ll
===================================================================
--- llvm/test/Transforms/LoopIdiom/basic.ll
+++ llvm/test/Transforms/LoopIdiom/basic.ll
@@ -1536,6 +1536,49 @@
   br i1 %cmp, label %for.body, label %for.cond.cleanup
 }
 
+; Do not form memmove when there's an aliasing operation, even
+; if the memcpy source and destination are in the same object.
+define void @do_not_form_memmove8(i64* %p) {
+; CHECK-LABEL: @do_not_form_memmove8(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[P2:%.*]] = getelementptr inbounds i64, i64* [[P:%.*]], i64 1000
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret void
+; CHECK:       loop:
+; CHECK-NEXT:    [[X4:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[X13:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[X5:%.*]] = zext i32 [[X4]] to i64
+; CHECK-NEXT:    [[X7:%.*]] = getelementptr inbounds i64, i64* [[P2]], i64 [[X5]]
+; CHECK-NEXT:    [[X8:%.*]] = bitcast i64* [[X7]] to i8*
+; CHECK-NEXT:    store i64 1, i64* [[X7]], align 4
+; CHECK-NEXT:    [[X11:%.*]] = getelementptr inbounds i64, i64* [[P]], i64 [[X5]]
+; CHECK-NEXT:    [[X12:%.*]] = bitcast i64* [[X11]] to i8*
+; CHECK-NEXT:    tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* [[X12]], i8* [[X8]], i64 8, i1 false)
+; CHECK-NEXT:    [[X13]] = add i32 [[X4]], 1
+; CHECK-NEXT:    [[X14:%.*]] = icmp eq i32 [[X13]], 44
+; CHECK-NEXT:    br i1 [[X14]], label [[EXIT:%.*]], label [[LOOP]]
+;
+entry:
+  %p2 = getelementptr inbounds i64, i64* %p, i64 1000
+  br label %loop
+
+exit:
+  ret void
+
+loop:
+  %x4 = phi i32 [ 0, %entry ], [ %x13, %loop ]
+  %x5 = zext i32 %x4 to i64
+  %x7 = getelementptr inbounds i64, i64* %p2, i64 %x5
+  %x8 = bitcast i64* %x7 to i8*
+  store i64 1, i64* %x7, align 4
+  %x11 = getelementptr inbounds i64, i64* %p, i64 %x5
+  %x12 = bitcast i64* %x11 to i8*
+  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %x12, i8* %x8, i64 8, i1 false)
+  %x13 = add i32 %x4, 1
+  %x14 = icmp eq i32 %x13, 44
+  br i1 %x14, label %exit, label %loop
+}
+
 ;; Memcpy formation is still preferred over memmove.
 define void @prefer_memcpy_over_memmove(i8* noalias %Src, i8* noalias %Dest, i64 %Size) {
 ; CHECK-LABEL: @prefer_memcpy_over_memmove(
Index: llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
+++ llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
@@ -1422,26 +1422,19 @@
 
   // If the store is a memcpy instruction, we must check if it will write to
   // the load memory locations. So remove it from the ignored stores.
-  if (IsMemCpy)
-    IgnoredInsts.erase(TheStore);
   MemmoveVerifier Verifier(*LoadBasePtr, *StoreBasePtr, *DL);
+  if (IsMemCpy && !Verifier.IsSameObject)
+    IgnoredInsts.erase(TheStore);
   if (mayLoopAccessLocation(LoadBasePtr, ModRefInfo::Mod, CurLoop, BECount,
                             StoreSizeSCEV, *AA, IgnoredInsts)) {
-    if (!IsMemCpy) {
-      ORE.emit([&]() {
-        return OptimizationRemarkMissed(DEBUG_TYPE, "LoopMayAccessLoad",
-                                        TheLoad)
-               << ore::NV("Inst", InstRemark) << " in "
-               << ore::NV("Function", TheStore->getFunction())
-               << " function will not be hoisted: "
-               << ore::NV("Reason", "The loop may access load location");
-      });
-      return Changed;
-    }
-    // At this point loop may access load only for memcpy in same underlying
-    // object. If that's not the case bail out.
-    if (!Verifier.IsSameObject)
-      return Changed;
+    ORE.emit([&]() {
+      return OptimizationRemarkMissed(DEBUG_TYPE, "LoopMayAccessLoad", TheLoad)
+             << ore::NV("Inst", InstRemark) << " in "
+             << ore::NV("Function", TheStore->getFunction())
+             << " function will not be hoisted: "
+             << ore::NV("Reason", "The loop may access load location");
+    });
+    return Changed;
   }
 
   bool UseMemMove = IsMemCpy ? Verifier.IsSameObject : LoopAccessStore;


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