[PATCH] D37121: [DivRemHoist] add a pass to move div/rem pairs into the same block (PR31028)

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

On closer inspection, I misdiagnosed who was sinking the rem in my example, but I don't think it makes a difference to the patch. We don't need loops to show the problem...if simplifycfg can't flatten the code, then it's instcombine sinking instructions for some unstated reason:

  define void @rebase_mask(i1 %cmp, i32 %num, i32 %divisor, i32* %p1, i32* %p2) {
  entry:
    %div = sdiv i32 %num, %divisor
    store i32 %div, i32* %p1
    br i1 %cmp, label %exit, label %if.end
  
  if.end:
    %rem = srem i32 %num, %divisor
    store i32 %rem, i32* %p2
    br label %exit
  
  exit:
    ret void
  }

./opt -div-rem-hoist -instcombine divrem.ll -S -debug 
...
	IC: Sink:   %rem = srem i32 %num, %divisor


https://reviews.llvm.org/D37121