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[DAGCombine]: Fold X/Sqrt(X) to Sqrt(X)

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With FMF ( "nsz" and " reassoc") fold X/Sqrt(X) to Sqrt(X).

This is done after targets have the chance to produce a
reciprocal sqrt estimate sequence because that expansion
is probably more efficient than an expansion of a
non-reciprocal sqrt. That is also why we deferred doing
this transform in IR (D85709).

Differential Revision: https://reviews.llvm.org/D86403
This commit is contained in:
Venkataramanan Kumar 2020-08-24 18:12:32 -04:00 committed by Sanjay Patel
parent 7a4b11cdee
commit 255be4506d
3 changed files with 20 additions and 23 deletions
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6
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@ -13356,6 +13356,12 @@ SDValue DAGCombiner::visitFDIV(SDNode *N) {
return RV;
}
// Fold X/Sqrt(X) -> Sqrt(X)
if ((Options.NoSignedZerosFPMath || Flags.hasNoSignedZeros()) &&
(Options.UnsafeFPMath || Flags.hasAllowReassociation()))
if (N1.getOpcode() == ISD::FSQRT && N0 == N1.getOperand(0))
return N1;
// (fdiv (fneg X), (fneg Y)) -> (fdiv X, Y)
TargetLowering::NegatibleCost CostN0 =
TargetLowering::NegatibleCost::Expensive;

13
test/CodeGen/AArch64/sqrt-fastmath.ll
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@ -448,8 +448,7 @@ define <4 x double> @d4rsqrt(<4 x double> %a) #0 {
define double @sqrt_fdiv_common_operand(double %x) nounwind {
; FAULT-LABEL: sqrt_fdiv_common_operand:
; FAULT: // %bb.0:
; FAULT-NEXT: fsqrt d1, d0
; FAULT-NEXT: fdiv d0, d0, d1
; FAULT-NEXT: fsqrt d0, d0
; FAULT-NEXT: ret
;
; CHECK-LABEL: sqrt_fdiv_common_operand:
@ -474,8 +473,7 @@ define double @sqrt_fdiv_common_operand(double %x) nounwind {
define <2 x double> @sqrt_fdiv_common_operand_vec(<2 x double> %x) nounwind {
; FAULT-LABEL: sqrt_fdiv_common_operand_vec:
; FAULT: // %bb.0:
; FAULT-NEXT: fsqrt v1.2d, v0.2d
; FAULT-NEXT: fdiv v0.2d, v0.2d, v1.2d
; FAULT-NEXT: fsqrt v0.2d, v0.2d
; FAULT-NEXT: ret
;
; CHECK-LABEL: sqrt_fdiv_common_operand_vec:
@ -493,16 +491,15 @@ define <2 x double> @sqrt_fdiv_common_operand_vec(<2 x double> %x) nounwind {
; CHECK-NEXT: fmul v0.2d, v0.2d, v1.2d
; CHECK-NEXT: ret
%sqrt = call <2 x double> @llvm.sqrt.v2f64(<2 x double> %x)
%r = fdiv nsz arcp reassoc <2 x double> %x, %sqrt
%r = fdiv arcp nsz reassoc <2 x double> %x, %sqrt
ret <2 x double> %r
}
define double @sqrt_fdiv_common_operand_extra_use(double %x, double* %p) nounwind {
; FAULT-LABEL: sqrt_fdiv_common_operand_extra_use:
; FAULT: // %bb.0:
; FAULT-NEXT: fsqrt d1, d0
; FAULT-NEXT: fdiv d0, d0, d1
; FAULT-NEXT: str d1, [x0]
; FAULT-NEXT: fsqrt d0, d0
; FAULT-NEXT: str d0, [x0]
; FAULT-NEXT: ret
;
; CHECK-LABEL: sqrt_fdiv_common_operand_extra_use:

24
test/CodeGen/X86/sqrt-fastmath.ll
View File

@ -903,14 +903,12 @@ define <4 x float> @div_sqrt_v4f32(<4 x float> %x, <4 x float> %y) {
define double @sqrt_fdiv_common_operand(double %x) nounwind {
; SSE-LABEL: sqrt_fdiv_common_operand:
; SSE: # %bb.0:
; SSE-NEXT: sqrtsd %xmm0, %xmm1
; SSE-NEXT: divsd %xmm1, %xmm0
; SSE-NEXT: sqrtsd %xmm0, %xmm0
; SSE-NEXT: retq
;
; AVX-LABEL: sqrt_fdiv_common_operand:
; AVX: # %bb.0:
; AVX-NEXT: vsqrtsd %xmm0, %xmm0, %xmm1
; AVX-NEXT: vdivsd %xmm1, %xmm0, %xmm0
; AVX-NEXT: vsqrtsd %xmm0, %xmm0, %xmm0
; AVX-NEXT: retq
%sqrt = call fast double @llvm.sqrt.f64(double %x)
%r = fdiv fast double %x, %sqrt
@ -920,33 +918,29 @@ define double @sqrt_fdiv_common_operand(double %x) nounwind {
define <2 x double> @sqrt_fdiv_common_operand_vec(<2 x double> %x) nounwind {
; SSE-LABEL: sqrt_fdiv_common_operand_vec:
; SSE: # %bb.0:
; SSE-NEXT: sqrtpd %xmm0, %xmm1
; SSE-NEXT: divpd %xmm1, %xmm0
; SSE-NEXT: sqrtpd %xmm0, %xmm0
; SSE-NEXT: retq
;
; AVX-LABEL: sqrt_fdiv_common_operand_vec:
; AVX: # %bb.0:
; AVX-NEXT: vsqrtpd %xmm0, %xmm1
; AVX-NEXT: vdivpd %xmm1, %xmm0, %xmm0
; AVX-NEXT: vsqrtpd %xmm0, %xmm0
; AVX-NEXT: retq
%sqrt = call <2 x double> @llvm.sqrt.v2f64(<2 x double> %x)
%r = fdiv nsz arcp reassoc <2 x double> %x, %sqrt
%r = fdiv arcp nsz reassoc <2 x double> %x, %sqrt
ret <2 x double> %r
}
define double @sqrt_fdiv_common_operand_extra_use(double %x, double* %p) nounwind {
; SSE-LABEL: sqrt_fdiv_common_operand_extra_use:
; SSE: # %bb.0:
; SSE-NEXT: sqrtsd %xmm0, %xmm1
; SSE-NEXT: movsd %xmm1, (%rdi)
; SSE-NEXT: divsd %xmm1, %xmm0
; SSE-NEXT: sqrtsd %xmm0, %xmm0
; SSE-NEXT: movsd %xmm0, (%rdi)
; SSE-NEXT: retq
;
; AVX-LABEL: sqrt_fdiv_common_operand_extra_use:
; AVX: # %bb.0:
; AVX-NEXT: vsqrtsd %xmm0, %xmm0, %xmm1
; AVX-NEXT: vmovsd %xmm1, (%rdi)
; AVX-NEXT: vdivsd %xmm1, %xmm0, %xmm0
; AVX-NEXT: vsqrtsd %xmm0, %xmm0, %xmm0
; AVX-NEXT: vmovsd %xmm0, (%rdi)
; AVX-NEXT: retq
%sqrt = call fast double @llvm.sqrt.f64(double %x)
store double %sqrt, double* %p