[PATCH] D51933: [AMDGPU] Ensure trig range reduction only used for subtargets that require it

[David Stuttard via Phabricator via llvm-commits]

dstuttard marked an inline comment as done.
dstuttard added inline comments.


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Comment at: lib/Target/AMDGPU/SIISelLowering.cpp:6655
+    SDValue MulVal = DAG.getNode(ISD::FMUL, DL, VT, Arg,
+                                 DAG.getConstantFP(0.5 / M_PI, DL, VT));
+    TrigVal = DAG.getNode(AMDGPUISD::FRACT, DL, VT, MulVal);
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arsenm wrote:
> dstuttard wrote:
> > arsenm wrote:
> > > Avoid repeating the same constant.
> > > 
> > > Also we should stop relying on system headers for these constants
> > Re system headers - why, are you concerned that M_PI may differ between compilers?
> > Can we defer removing reliance on system headers to a separate change that does this globally?
> Yes. AFAIK the standard doesn't actually specify the exact rounded value. For other system provided constants, LLVM usually duplicates the definitions and puts them in Support
That's a reasonable point. 

However, would you mind if I defer that to a different change as making changes in Support will spill this change over into a core change - the old code used M_PI before, so it's no worse as it stands.


Repository:
  rL LLVM

https://reviews.llvm.org/D51933