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[DAGCombiner] Don't combine (addcarry (uaddo X, Y), 0, Carry) -> (addcarry X, Y, Carry) if the Carry comes from the uaddo.

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Summary:
The uaddo won't be removed and the addcarry will still be
dependent on the uaddo. So we'll just increase the use count
of X and Y and potentially require a COPY.

Reviewers: spatel, RKSimon, deadalnix

Reviewed By: RKSimon

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D64190

llvm-svn: 365149
This commit is contained in:
Craig Topper 2019-07-04 18:18:46 +00:00
parent dd229b271a
commit 20330a7c7f
2 changed files with 6 additions and 5 deletions
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5
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
View File

@ -2966,8 +2966,11 @@ SDValue DAGCombiner::visitADDCARRYLike(SDValue N0, SDValue N1, SDValue CarryIn,
SDNode *N) {
// Iff the flag result is dead:
// (addcarry (add|uaddo X, Y), 0, Carry) -> (addcarry X, Y, Carry)
// Don't do this if the Carry comes from the uaddo. It won't remove the uaddo
// or the dependency between the instructions.
if ((N0.getOpcode() == ISD::ADD ||
(N0.getOpcode() == ISD::UADDO && N0.getResNo() == 0)) &&
(N0.getOpcode() == ISD::UADDO && N0.getResNo() == 0 &&
N0.getValue(1) != CarryIn)) &&
isNullConstant(N1) && !N->hasAnyUseOfValue(1))
return DAG.getNode(ISD::ADDCARRY, SDLoc(N), N->getVTList(),
N0.getOperand(0), N0.getOperand(1), CarryIn);

6
test/CodeGen/X86/add-of-carry.ll
View File

@ -9,11 +9,9 @@
define i32 @test1(i32 %sum, i32 %x) nounwind readnone ssp {
; CHECK-LABEL: test1:
; CHECK: # %bb.0:
; CHECK-NEXT: movl {{[0-9]+}}(%esp), %ecx
; CHECK-NEXT: movl {{[0-9]+}}(%esp), %eax
; CHECK-NEXT: movl %eax, %edx
; CHECK-NEXT: addl %ecx, %edx
; CHECK-NEXT: adcl %ecx, %eax
; CHECK-NEXT: addl {{[0-9]+}}(%esp), %eax
; CHECK-NEXT: adcl $0, %eax
; CHECK-NEXT: retl
%add4 = add i32 %x, %sum
%cmp = icmp ult i32 %add4, %x