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According to IR LangRef, the FMF flag: contract Allow floating-point contraction (e.g. fusing a multiply followed by an addition into a fused multiply-and-add). reassoc Allow reassociation transformations for floating-point instructions. This may dramatically change results in floating-point. My understanding is that these two flags shouldn't imply each other, as we might have a SDNode that can be reassociated with others, but not contractble. eg: We may want following fmul/fad/fsub to freely reassoc, but don't want fma being generated here. %F = fmul reassoc double %A, %B ; <double> [#uses=1] %G = fmul reassoc double %C, %D ; <double> [#uses=1] %H = fadd reassoc double %F, %G ; <double> [#uses=1] %I = fsub reassoc double %H, %E ; <double> [#uses=1] Before https://reviews.llvm.org/D45710, `reassoc` flag actually did not imply isContratable either. The current implementation also only check the flag in fadd node, ignoring fmul node, this patch update that as well. Reviewed By: spatel, qiucf Differential Revision: https://reviews.llvm.org/D104247
36 lines
1.3 KiB
LLVM
36 lines
1.3 KiB
LLVM
; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
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; RUN: llc < %s -verify-machineinstrs -mtriple=powerpc64le-linux-gnu | FileCheck %s
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define float @can_fma_with_fewer_uses(float %f1, float %f2, float %f3, float %f4) {
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; CHECK-LABEL: can_fma_with_fewer_uses:
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; CHECK: # %bb.0:
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; CHECK-NEXT: xsmulsp 0, 1, 2
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; CHECK-NEXT: fmr 1, 0
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; CHECK-NEXT: xsmaddasp 1, 3, 4
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; CHECK-NEXT: xsdivsp 1, 0, 1
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; CHECK-NEXT: blr
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%mul1 = fmul contract float %f1, %f2
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%mul2 = fmul contract float %f3, %f4
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%add = fadd contract float %mul1, %mul2
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%second_use_of_mul1 = fdiv float %mul1, %add
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ret float %second_use_of_mul1
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}
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; There is no contract on the mul with no extra use so we can't fuse that.
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; Since we are fusing with the mul with an extra use, the fmul needs to stick
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; around beside the fma.
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define float @no_fma_with_fewer_uses(float %f1, float %f2, float %f3, float %f4) {
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; CHECK-LABEL: no_fma_with_fewer_uses:
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; CHECK: # %bb.0:
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; CHECK-NEXT: xsmulsp 0, 3, 4
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; CHECK-NEXT: xsmulsp 3, 1, 2
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; CHECK-NEXT: xsmaddasp 0, 1, 2
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; CHECK-NEXT: xsdivsp 1, 3, 0
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; CHECK-NEXT: blr
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%mul1 = fmul contract float %f1, %f2
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%mul2 = fmul float %f3, %f4
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%add = fadd contract float %mul1, %mul2
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%second_use_of_mul1 = fdiv float %mul1, %add
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ret float %second_use_of_mul1
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}
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