[PATCH] D67553: [InstSimplify] Match 1.0 and 0.0 for both operands in SimplifyFMAMul

[Philip Reames via Phabricator via llvm-commits]

reames added inline comments.


================
Comment at: llvm/lib/Analysis/InstructionSimplify.cpp:4561
                               const SimplifyQuery &Q, unsigned MaxRecurse) {
   // fmul X, 1.0 ==> X
   if (match(Op1, m_FPOne()))
----------------
reames wrote:
> fhahn wrote:
> > lebedev.ri wrote:
> > > I'm wondering if 
> > > ```
> > > {
> > > if(isa<Constant>(Op0)) std::swap(Op0, Op1);
> > > ```
> > > would be simpler?
> > I initially also used to swap the operands, but we'd also have to check if it's a 1.1 or 0.0 constant I think, to handle `fmul 10.0, 0.0`. That's not a problem with SimplifyFMulInst, as constant folding would cover this case.
> I believe that fmul is not necessarily commutative (for nan inputs).  Given that, swap would be correct for this case, but dangerous in general.
Er, maybe I'm wrong here.  At least the accessors in Instruction.h seems to think so.  


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https://reviews.llvm.org/D67553