[PATCH] D142387: [SCCP] Use range info to prove AddInst has NUW flag.

[Nikita Popov via Phabricator via llvm-commits]

nikic added inline comments.


================
Comment at: llvm/lib/Transforms/Utils/SCCPSolver.cpp:191
+    auto RangeB = GetRange(Inst.getOperand(1));
+    auto NUWRange = ConstantRange::makeGuaranteedNoWrapRegion(
+        Instruction::Add, RangeB, OverflowingBinaryOperator::NoUnsignedWrap);
----------------
fhahn wrote:
> nikic wrote:
> > This should be guarded under `if (!Inst.hasNoUnsignedWrap())`. Otherwise we will report an unnecessary change.
> Thanks, changed to  `if (!Inst.hasNoUnsignedWrap() &&NUWRange.contains(RangeA))`. Could also have a separate check guarding `makeGuaranteedNoWrapRegion`, which would increase nesting though and hopefully existing compilers should be smart enough to delay the computation :)
> 
Existing compilers almost certainly can't delay that computation (it's not LLVM_READONLY, and I'm not sure clang would sink the call even then).


Repository:
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CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D142387/new/

https://reviews.llvm.org/D142387