[PATCH] D43079: [TTI CostModel] change default cost of FP ops to 1 (PR36280)

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

In https://reviews.llvm.org/D43079#1013835, @anemet wrote:

> Please revert until these things get worked out so that we can properly track performance.   We are seeing many regressions including 17% on 444.namd and 12% on 482.sphinx3 in SPECfp 2006.


Hi Adam -

Rather than reverting for all targets, can we just hack ARM/AArch with patches like this (if we can add at least one test to show what changed, that would be better of course) :

  Index: lib/Target/ARM/ARMTargetTransformInfo.cpp
  ===================================================================
  --- lib/Target/ARM/ARMTargetTransformInfo.cpp	(revision 325579)
  +++ lib/Target/ARM/ARMTargetTransformInfo.cpp	(working copy)
  @@ -514,6 +514,13 @@
     int Cost = BaseT::getArithmeticInstrCost(Opcode, Ty, Op1Info, Op2Info,
                                              Opd1PropInfo, Opd2PropInfo);
   
  +  // Assume that floating point arithmetic operations cost twice as much as
  +  // integer operations.
  +  // FIXME: This is a win on several perf benchmarks running on CPU model ???,
  +  // but there are no regression tests that show why or how this is good.
  +  if (Ty->isFPOrFPVectorTy())
  +    Cost *= 2;
  +
     // This is somewhat of a hack. The problem that we are facing is that SROA
     // creates a sequence of shift, and, or instructions to construct values.
     // These sequences are recognized by the ISel and have zero-cost. Not so for


Repository:
  rL LLVM

https://reviews.llvm.org/D43079