[PATCH] D109201: [AMDGPU] Process any power of 2 in optimizeCompareInstr

[Stanislav Mekhanoshin via Phabricator via llvm-commits]

rampitec added inline comments.


================
Comment at: llvm/lib/Target/AMDGPU/SIInstrInfo.cpp:8036
+    //
+    // Signed ge/gt are not used for the sign bit.
     //
----------------
foad wrote:
> Yeah that is an ugly special case. Do we really need to handle ge/gt here at all? Can't we rely on something else canonicalizing them all to eq/ne comparisons?
It must be even uglier since llvm tends to change "a >= i" to "a > i - 1". So in practice it is canonicacalized to be not a power of 2 often. That is really so much interlinked...

In addition it tends to kill any known power of 2 by replacing it with a shift and comparing a low bit. I feel somewhat lost trying to deoptimize.


================
Comment at: llvm/lib/Target/AMDGPU/SIInstrInfo.cpp:8119
       .add(*SrcOp)
-      .addImm(0);
+      .addImm(Log2_64(Mask));
     Def->eraseFromParent();
----------------
foad wrote:
> Isn't this just `BitNo`?
Yes, silly. Too much changes and copy-paste.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D109201/new/

https://reviews.llvm.org/D109201