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X86: optimized i64 vector multiply with constant

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When we multiply two 64-bit vectors, we extract lower and upper part and use the PMULUDQ instruction.
When one of the operands is a constant, the upper part may be zero, we know this at compile time.
Example: %a = mul <4 x i64> %b, <4 x i64> < i64 5, i64 5, i64 5, i64 5>.
I'm checking the value of the upper part and prevent redundant "multiply", "shift" and "add" operations.

llvm-svn: 239802
This commit is contained in:
Elena Demikhovsky 2015-06-16 06:07:24 +00:00
parent b603d53f5d
commit 7cf9dd07b7
2 changed files with 44 additions and 9 deletions
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16
lib/Target/X86/X86ISelLowering.cpp
View File

@ -16530,6 +16530,8 @@ static SDValue LowerMUL(SDValue Op, const X86Subtarget *Subtarget,
SDValue Ahi = getTargetVShiftByConstNode(X86ISD::VSRLI, dl, VT, A, 32, DAG);
SDValue Bhi = getTargetVShiftByConstNode(X86ISD::VSRLI, dl, VT, B, 32, DAG);
SDValue AhiBlo = Ahi;
SDValue AloBhi = Bhi;
// Bit cast to 32-bit vectors for MULUDQ
EVT MulVT = (VT == MVT::v2i64) ? MVT::v4i32 :
(VT == MVT::v4i64) ? MVT::v8i32 : MVT::v16i32;
@ -16539,11 +16541,15 @@ static SDValue LowerMUL(SDValue Op, const X86Subtarget *Subtarget,
Bhi = DAG.getBitcast(MulVT, Bhi);
SDValue AloBlo = DAG.getNode(X86ISD::PMULUDQ, dl, VT, A, B);
SDValue AloBhi = DAG.getNode(X86ISD::PMULUDQ, dl, VT, A, Bhi);
SDValue AhiBlo = DAG.getNode(X86ISD::PMULUDQ, dl, VT, Ahi, B);
AloBhi = getTargetVShiftByConstNode(X86ISD::VSHLI, dl, VT, AloBhi, 32, DAG);
AhiBlo = getTargetVShiftByConstNode(X86ISD::VSHLI, dl, VT, AhiBlo, 32, DAG);
// After shifting right const values the result may be all-zero.
if (!ISD::isBuildVectorAllZeros(Ahi.getNode())) {
AhiBlo = DAG.getNode(X86ISD::PMULUDQ, dl, VT, Ahi, B);
AhiBlo = getTargetVShiftByConstNode(X86ISD::VSHLI, dl, VT, AhiBlo, 32, DAG);
}
if (!ISD::isBuildVectorAllZeros(Bhi.getNode())) {
AloBhi = DAG.getNode(X86ISD::PMULUDQ, dl, VT, A, Bhi);
AloBhi = getTargetVShiftByConstNode(X86ISD::VSHLI, dl, VT, AloBhi, 32, DAG);
}
SDValue Res = DAG.getNode(ISD::ADD, dl, VT, AloBlo, AloBhi);
return DAG.getNode(ISD::ADD, dl, VT, Res, AhiBlo);

37
test/CodeGen/X86/pmul.ll
View File

@ -1,5 +1,6 @@
; RUN: llc < %s -mtriple=x86_64-unknown-unknown | FileCheck %s --check-prefix=ALL --check-prefix=SSE2
; RUN: llc < %s -mtriple=x86_64-unknown-unknown -mattr=sse4.1 | FileCheck %s --check-prefix=ALL --check-prefix=SSE41
; RUN: llc < %s -mtriple=x86_64-unknown-unknown -mcpu=core-avx2 | FileCheck %s --check-prefix=AVX2
define <16 x i8> @mul8c(<16 x i8> %i) nounwind {
; SSE2-LABEL: mul8c:
@ -75,10 +76,6 @@ define <2 x i64> @b(<2 x i64> %i) nounwind {
; ALL-NEXT: movdqa {{.*#+}} xmm1 = [117,117]
; ALL-NEXT: movdqa %xmm0, %xmm2
; ALL-NEXT: pmuludq %xmm1, %xmm2
; ALL-NEXT: pxor %xmm3, %xmm3
; ALL-NEXT: pmuludq %xmm0, %xmm3
; ALL-NEXT: psllq $32, %xmm3
; ALL-NEXT: paddq %xmm3, %xmm2
; ALL-NEXT: psrlq $32, %xmm0
; ALL-NEXT: pmuludq %xmm1, %xmm0
; ALL-NEXT: psllq $32, %xmm0
@ -248,3 +245,35 @@ entry:
%A = mul <2 x i64> %i, %j
ret <2 x i64> %A
}
define <4 x i64> @b1(<4 x i64> %i) nounwind {
; AVX2-LABEL: @b1
; AVX2: vpbroadcastq
; AVX2-NEXT: vpmuludq
; AVX2-NEXT: vpsrlq $32
; AVX2-NEXT: vpmuludq
; AVX2-NEXT: vpsllq $32
; AVX2-NEXT: vpaddq
; AVX2-NEXT: retq
entry:
%A = mul <4 x i64> %i, < i64 117, i64 117, i64 117, i64 117 >
ret <4 x i64> %A
}
define <4 x i64> @b2(<4 x i64> %i, <4 x i64> %j) nounwind {
; AVX2-LABEL: @b2
; AVX2: vpmuludq
; AVX2-NEXT: vpsrlq $32
; AVX2-NEXT: vpmuludq
; AVX2-NEXT: vpsllq $32
; AVX2-NEXT: vpaddq
; AVX2-NEXT: vpsrlq $32
; AVX2-NEXT: vpmuludq
; AVX2-NEXT: vpsllq $32
; AVX2-NEXT: vpaddq
; AVX2-NEXT: retq
entry:
%A = mul <4 x i64> %i, %j
ret <4 x i64> %A
}