[PATCH] D96614: [AMDGPU][GlobalISel] Transform (fsub (fmul x, y), z) -> (fma x, y, -z)

[Mateja Marjanovic via Phabricator via llvm-commits]

matejam added a comment.

In D96614#2787052 <https://reviews.llvm.org/D96614#2787052>, @foad wrote:

> Does this assume that all targets can do the fneg for free? Or can a target choose to fold only `(fadd (fmul x, y), z)`, not `(fsub (fmul x, y), z)` ?

Similar to SelectionDAG which negates an SDValue:

  fold (fsub (fmul x, y), z) -> (fma x, y, (fneg z))
  DAG.getNode(PreferredFusedOpcode, SL, VT, XY.getOperand(0),
              XY.getOperand(1), DAG.getNode(ISD::FNEG, SL, VT, Z));


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  https://reviews.llvm.org/D96614/new/

https://reviews.llvm.org/D96614