[PATCH] D155461: [InstCombine] Keep !unpredictable when combining select+add

Tue Jul 18 08:49:47 PDT 2023

goldstein.w.n added inline comments.

================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp:540
       Value *NewSel = Builder.CreateSelect(SI.getCondition(), Swapped ? C : OOp,
-                                           Swapped ? OOp : C);
+                                           Swapped ? OOp : C, "", &SI);
       if (isa<FPMathOperator>(&SI))
----------------
chfast wrote:
> goldstein.w.n wrote:
> > chfast wrote:
> > > I believe there are more case in the file where metadata copy is missed. I will try to identify them and create more tests cases. Can be in this review on later, depending on reviewers' suggestion.
> > Are there any other binops you want to preserve this flag for?
> I think it make sense for any binop because the condition of the select in this transformation remains unchanged (i.e. `!unpredictable` is still applicable).
I think you have this in the right place for most binops, but you should probably add additional tests for things like:
`sub`, `or`, `xor`, `and`, `mul`, `div`, `rem`, `llvm.min`, `llvm.max`, etc...

you probably don't need all but some variety of those (like 1/2 bitwise, div or rem, a few intrinsics) should provide better coverage.

================
Comment at: llvm/test/Transforms/InstCombine/unpredictable-select.ll:1
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt < %s -passes=instcombine -S | FileCheck %s
----------------
nikic wrote:
> goldstein.w.n wrote:
> > chfast wrote:
> > > I created this test file. Is this good location?
> > Its fine.
> I would add this to the select_meta.ll test.
+1

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D155461/new/

https://reviews.llvm.org/D155461