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
Summary:
This is follow up patch of https://reviews.llvm.org/D67595.
Adjust naming and the Commutable operands for additional patterns
to make it easier to read.
The testcase update also show that we can save some unecessary fmr as
well.
Reviewers: #powerpc, steven.zhang, hfinkel, nemanjai
Reviewed By: #powerpc, nemanjai
Subscribers: wuzish, hiraditya, kbarton, MaskRay, shchenz, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D68112
llvm-svn: 373652
Lei Huang