[llvm] 3e37543 - [MemCpyOpt] Move GEP during call slot optimization
Nikita Popov via llvm-commits
llvm-commits at lists.llvm.org
Thu Oct 22 11:41:06 PDT 2020
Author: Nikita Popov
Date: 2020-10-22T20:40:56+02:00
New Revision: 3e37543111f40c3fa2430a80eb0293ae3b814dd3
URL: https://github.com/llvm/llvm-project/commit/3e37543111f40c3fa2430a80eb0293ae3b814dd3
DIFF: https://github.com/llvm/llvm-project/commit/3e37543111f40c3fa2430a80eb0293ae3b814dd3.diff
LOG: [MemCpyOpt] Move GEP during call slot optimization
When performing a call slot optimization to a GEP destination, it
will currently usually fail, because the GEP is directly before the
memcpy and as such does not dominate the call. We should move it
above the call if that satisfies the domination requirement.
I think that a constant-index GEP is the only useful thing to move
here, as otherwise isDereferenceablePointer couldn't look through
it anyway. As such I'm not trying to generalize this further.
Differential Revision: https://reviews.llvm.org/D89623
Added:
Modified:
llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
llvm/test/Transforms/MemCpyOpt/callslot.ll
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
index d8a2f55957b1..a08a1a7f515e 100644
--- a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -913,10 +913,15 @@ bool MemCpyOptPass::performCallSlotOptzn(Instruction *cpyLoad,
// 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
diff --git a/llvm/test/Transforms/MemCpyOpt/callslot.ll b/llvm/test/Transforms/MemCpyOpt/callslot.ll
index 37a3cdea88e5..f85a67667950 100644
--- a/llvm/test/Transforms/MemCpyOpt/callslot.ll
+++ b/llvm/test/Transforms/MemCpyOpt/callslot.ll
@@ -150,9 +150,10 @@ define void @dest_is_gep_requires_movement() {
; 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]
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