[PATCH] D64713: [InstCombine] X *fast (C ? 1.0 : 0.0) -> C ? X : 0.0

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added a comment.

In D64713#1604369 <https://reviews.llvm.org/D64713#1604369>, @xbolva00 wrote:

> Do we miss int version of this? @spatel @lebedev.ri
>
>   int foo(int x, int y, bool b) {
>       return x / (b  ? 1 : y);
>   }
>
>
> We have sdiv x, (select b 1 y), x86-64:
>  cmov...
>  idiv...


I'd agree that having `select %b (div %x, %y), %x` would be better but that does not look like a valid transform:
https://godbolt.org/z/4Fs_dB
https://rise4fun.com/Alive/xplW

  Optimization: D64713-int
  
  ERROR: Domain of definedness of Target is smaller than Source's for i32 %r
  
  Example:
  %b i1 = 0x1 (1, -1)
  %y i32 = poison
  %x i32 = poison
  %cond i32 = 0x00000001 (1)
  %t0 i32 = UB
  Source value: poison
  Target value: UB

  $ /repositories/alive2/build-Clang-unknown/alive -root-only /tmp/test.ll 
  Processing /tmp/test.ll..
  
  ----------------------------------------
  Name: D64713-int
    %cond = select i1 %b, i8 1, i8 %y
    %r = sdiv i8 %x, %cond
    ret i8 %r
  =>
    %cond = select i1 %b, i8 1, i8 %y
    %t0 = sdiv i8 %x, %y
    %r = select i1 %b, i8 %x, i8 %t0
    ret i8 %r
  
  ERROR: Source is more defined than target
  
  Example:
  i1 %b = #x1 (1)
  i8 %y = poison
  i8 %x = poison
  
  Source:
  i8 %cond = #x01 (1)
  i8 %r = poison
  
  Target:
  i8 %cond = #x01 (1)
  i8 %t0 = poison
  i8 %r = poison


Repository:
  rG LLVM Github Monorepo

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https://reviews.llvm.org/D64713