[PATCH] D89623: [MemCpyOpt] Move GEP during call slot optimization

[Nikita Popov via Phabricator via llvm-commits]

nikic updated this revision to Diff 300029.
nikic added a comment.

Rebase over generalized dominates() API.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D89623/new/

https://reviews.llvm.org/D89623

Files:
  llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
  llvm/test/Transforms/MemCpyOpt/callslot.ll


Index: llvm/test/Transforms/MemCpyOpt/callslot.ll
===================================================================
--- llvm/test/Transforms/MemCpyOpt/callslot.ll
+++ llvm/test/Transforms/MemCpyOpt/callslot.ll
@@ -150,9 +150,10 @@
 ; CHECK-NEXT:    [[DEST:%.*]] = alloca [16 x i8], align 1
 ; CHECK-NEXT:    [[SRC:%.*]] = alloca [8 x i8], align 1
 ; CHECK-NEXT:    [[SRC_I8:%.*]] = bitcast [8 x i8]* [[SRC]] to i8*
-; CHECK-NEXT:    call void @accept_ptr(i8* [[SRC_I8]]) [[ATTR3]]
 ; CHECK-NEXT:    [[DEST_I8:%.*]] = getelementptr [16 x i8], [16 x i8]* [[DEST]], i64 0, i64 8
-; CHECK-NEXT:    call void @llvm.memcpy.p0i8.p0i8.i64(i8* [[DEST_I8]], i8* [[SRC_I8]], i64 8, i1 false)
+; CHECK-NEXT:    [[DEST_I81:%.*]] = bitcast i8* [[DEST_I8]] to [8 x i8]*
+; CHECK-NEXT:    [[DEST_I812:%.*]] = bitcast [8 x i8]* [[DEST_I81]] to i8*
+; CHECK-NEXT:    call void @accept_ptr(i8* [[DEST_I812]]) [[ATTR3]]
 ; CHECK-NEXT:    ret void
 ;
   %dest = alloca [16 x i8]
Index: llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -913,10 +913,15 @@
 
   // Since we're changing the parameter to the callsite, we need to make sure
   // that what would be the new parameter dominates the callsite.
-  // TODO: Support moving instructions like GEPs upwards.
-  if (Instruction *cpyDestInst = dyn_cast<Instruction>(cpyDest))
-    if (!DT->dominates(cpyDestInst, C))
+  if (!DT->dominates(cpyDest, C)) {
+    // Support moving a constant index GEP before the call.
+    auto *GEP = dyn_cast<GetElementPtrInst>(cpyDest);
+    if (GEP && GEP->hasAllConstantIndices() &&
+        DT->dominates(GEP->getPointerOperand(), C))
+      GEP->moveBefore(C);
+    else
       return false;
+  }
 
   // In addition to knowing that the call does not access src in some
   // unexpected manner, for example via a global, which we deduce from


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