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
On PowerPC, FNMSUB (both VSX and non-VSX version) means -(a*b-c). But
the backend used to generate these instructions regardless whether nsz
flag exists or not. If a*b-c==0, such transformation changes sign of
zero.
This patch introduces PPC specific FNMSUB ISD opcode, which may help
improving combined FMA code sequence.
Reviewed By: steven.zhang
Differential Revision: https://reviews.llvm.org/D76585
A lot of tests under PowerPC are using fast flag, while fast is just
alias of 7 fast-math flags. This change makes test points clearer.
mc-instrlat.ll and sms-iterator.ll keeps unchanged since they are not
testing fast-math behavior. (one for machine combiner crash, one for
machine pipeliner bug)
Reviewed By: steven.zhang, spatel
Differential Revision: https://reviews.llvm.org/D78989
If it is a*b-c*d, it could be also folded into fma(a, b, -c*d) or fma(-c, d, a*b).
This patch is trying to respect the uses of a*b and c*d to make the best choice.
Differential Revision: https://reviews.llvm.org/D75982
Jinsong Ji