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[SelectionDAG] fold constant with undef vector per element

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This makes the SDAG behavior consistent with the way we do this in IR.
It's possible that we were getting the wrong answer before. For example,
'xor undef, undef --> 0' but 'xor undef, C' --> undef. 

But the most practical improvement is likely as shown in the tests here - 
for FP, we were overconstraining undef lanes to NaN, and that can prevent 
vector simplifications/narrowing (see D51553).

llvm-svn: 348090
This commit is contained in:
Sanjay Patel 2018-12-02 13:48:42 +00:00
parent 7fad8e54d1
commit 2986f40e8a
2 changed files with 26 additions and 20 deletions
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26
lib/CodeGen/SelectionDAG/SelectionDAG.cpp
View File

@ -4400,14 +4400,20 @@ SDValue SelectionDAG::FoldConstantArithmetic(unsigned Opcode, const SDLoc &DL,
if (GlobalAddressSDNode *GA = dyn_cast<GlobalAddressSDNode>(Cst2))
return FoldSymbolOffset(Opcode, VT, GA, Cst1);
// For vectors extract each constant element into Inputs so we can constant
// fold them individually.
BuildVectorSDNode *BV1 = dyn_cast<BuildVectorSDNode>(Cst1);
BuildVectorSDNode *BV2 = dyn_cast<BuildVectorSDNode>(Cst2);
if (!BV1 || !BV2)
// For vectors, extract each constant element and fold them individually.
// Either input may be an undef value.
auto *BV1 = dyn_cast<BuildVectorSDNode>(Cst1);
if (!BV1 && !Cst1->isUndef())
return SDValue();
auto *BV2 = dyn_cast<BuildVectorSDNode>(Cst2);
if (!BV2 && !Cst2->isUndef())
return SDValue();
// If both operands are undef, that's handled the same way as scalars.
if (!BV1 && !BV2)
return SDValue();
assert(BV1->getNumOperands() == BV2->getNumOperands() && "Out of sync!");
assert((!BV1 || !BV2 || BV1->getNumOperands() == BV2->getNumOperands()) &&
"Vector binop with different number of elements in operands?");
EVT SVT = VT.getScalarType();
EVT LegalSVT = SVT;
@ -4417,10 +4423,10 @@ SDValue SelectionDAG::FoldConstantArithmetic(unsigned Opcode, const SDLoc &DL,
return SDValue();
}
SmallVector<SDValue, 4> Outputs;
for (unsigned I = 0, E = BV1->getNumOperands(); I != E; ++I) {
SDValue V1 = BV1->getOperand(I);
SDValue V2 = BV2->getOperand(I);
unsigned NumOps = BV1 ? BV1->getNumOperands() : BV2->getNumOperands();
for (unsigned I = 0; I != NumOps; ++I) {
SDValue V1 = BV1 ? BV1->getOperand(I) : getUNDEF(SVT);
SDValue V2 = BV2 ? BV2->getOperand(I) : getUNDEF(SVT);
if (SVT.isInteger()) {
if (V1->getValueType(0).bitsGT(SVT))
V1 = getNode(ISD::TRUNCATE, DL, SVT, V1);

20
test/CodeGen/X86/fp-undef.ll
View File

@ -508,7 +508,7 @@ define double @frem_undef_op1_fast_constant_inf(double %x) {
define <2 x double> @fadd_undef_op1_constant_vec(<2 x double> %x) {
; ANY-LABEL: fadd_undef_op1_constant_vec:
; ANY: # %bb.0:
; ANY-NEXT: movaps {{.*#+}} xmm0 = [NaN,NaN]
; ANY-NEXT: movsd {{.*#+}} xmm0 = mem[0],zero
; ANY-NEXT: retq
%r = fadd <2 x double> <double 42.0, double undef>, undef
ret <2 x double> %r
@ -517,7 +517,7 @@ define <2 x double> @fadd_undef_op1_constant_vec(<2 x double> %x) {
define <2 x double> @fadd_undef_op0_constant_vec(<2 x double> %x) {
; ANY-LABEL: fadd_undef_op0_constant_vec:
; ANY: # %bb.0:
; ANY-NEXT: movaps {{.*#+}} xmm0 = [NaN,NaN]
; ANY-NEXT: movaps {{.*#+}} xmm0 = <u,NaN>
; ANY-NEXT: retq
%r = fadd <2 x double> undef, <double undef, double 42.0>
ret <2 x double> %r
@ -526,7 +526,7 @@ define <2 x double> @fadd_undef_op0_constant_vec(<2 x double> %x) {
define <2 x double> @fsub_undef_op1_constant_vec(<2 x double> %x) {
; ANY-LABEL: fsub_undef_op1_constant_vec:
; ANY: # %bb.0:
; ANY-NEXT: movaps {{.*#+}} xmm0 = [NaN,NaN]
; ANY-NEXT: movaps {{.*#+}} xmm0 = <u,NaN>
; ANY-NEXT: retq
%r = fsub <2 x double> <double undef, double 42.0>, undef
ret <2 x double> %r
@ -535,7 +535,7 @@ define <2 x double> @fsub_undef_op1_constant_vec(<2 x double> %x) {
define <2 x double> @fsub_undef_op0_constant_vec(<2 x double> %x) {
; ANY-LABEL: fsub_undef_op0_constant_vec:
; ANY: # %bb.0:
; ANY-NEXT: movaps {{.*#+}} xmm0 = [NaN,NaN]
; ANY-NEXT: movsd {{.*#+}} xmm0 = mem[0],zero
; ANY-NEXT: retq
%r = fsub <2 x double> undef, <double 42.0, double undef>
ret <2 x double> %r
@ -544,7 +544,7 @@ define <2 x double> @fsub_undef_op0_constant_vec(<2 x double> %x) {
define <2 x double> @fmul_undef_op1_constant_vec(<2 x double> %x) {
; ANY-LABEL: fmul_undef_op1_constant_vec:
; ANY: # %bb.0:
; ANY-NEXT: movaps {{.*#+}} xmm0 = [NaN,NaN]
; ANY-NEXT: movsd {{.*#+}} xmm0 = mem[0],zero
; ANY-NEXT: retq
%r = fmul <2 x double> <double 42.0, double undef>, undef
ret <2 x double> %r
@ -553,7 +553,7 @@ define <2 x double> @fmul_undef_op1_constant_vec(<2 x double> %x) {
define <2 x double> @fmul_undef_op0_constant_vec(<2 x double> %x) {
; ANY-LABEL: fmul_undef_op0_constant_vec:
; ANY: # %bb.0:
; ANY-NEXT: movaps {{.*#+}} xmm0 = [NaN,NaN]
; ANY-NEXT: movaps {{.*#+}} xmm0 = <u,NaN>
; ANY-NEXT: retq
%r = fmul <2 x double> undef, <double undef, double 42.0>
ret <2 x double> %r
@ -562,7 +562,7 @@ define <2 x double> @fmul_undef_op0_constant_vec(<2 x double> %x) {
define <2 x double> @fdiv_undef_op1_constant_vec(<2 x double> %x) {
; ANY-LABEL: fdiv_undef_op1_constant_vec:
; ANY: # %bb.0:
; ANY-NEXT: movaps {{.*#+}} xmm0 = [NaN,NaN]
; ANY-NEXT: movsd {{.*#+}} xmm0 = mem[0],zero
; ANY-NEXT: retq
%r = fdiv <2 x double> <double 42.0, double undef>, undef
ret <2 x double> %r
@ -571,7 +571,7 @@ define <2 x double> @fdiv_undef_op1_constant_vec(<2 x double> %x) {
define <2 x double> @fdiv_undef_op0_constant_vec(<2 x double> %x) {
; ANY-LABEL: fdiv_undef_op0_constant_vec:
; ANY: # %bb.0:
; ANY-NEXT: movaps {{.*#+}} xmm0 = [NaN,NaN]
; ANY-NEXT: movaps {{.*#+}} xmm0 = <u,NaN>
; ANY-NEXT: retq
%r = fdiv <2 x double> undef, <double undef, double 42.0>
ret <2 x double> %r
@ -580,7 +580,7 @@ define <2 x double> @fdiv_undef_op0_constant_vec(<2 x double> %x) {
define <2 x double> @frem_undef_op1_constant_vec(<2 x double> %x) {
; ANY-LABEL: frem_undef_op1_constant_vec:
; ANY: # %bb.0:
; ANY-NEXT: movaps {{.*#+}} xmm0 = [NaN,NaN]
; ANY-NEXT: movaps {{.*#+}} xmm0 = <u,NaN>
; ANY-NEXT: retq
%r = frem <2 x double> <double undef, double 42.0>, undef
ret <2 x double> %r
@ -589,7 +589,7 @@ define <2 x double> @frem_undef_op1_constant_vec(<2 x double> %x) {
define <2 x double> @frem_undef_op0_constant_vec(<2 x double> %x) {
; ANY-LABEL: frem_undef_op0_constant_vec:
; ANY: # %bb.0:
; ANY-NEXT: movaps {{.*#+}} xmm0 = [NaN,NaN]
; ANY-NEXT: movsd {{.*#+}} xmm0 = mem[0],zero
; ANY-NEXT: retq
%r = frem <2 x double> undef, <double 42.0, double undef>
ret <2 x double> %r