[PATCH] D153660: [ConstraintElim] Track and simplify conditions at use.

[Florian Hahn via Phabricator via llvm-commits]

fhahn updated this revision to Diff 534967.
fhahn added a comment.

Address latest comments, thanks!

In D153660#4452297 <https://reviews.llvm.org/D153660#4452297>, @nikic wrote:

> Can you please also add a test along these lines?
>
>   define i1 @test(i1 %c, i32 %x) {
>   entry:
>     br i1 %c, label %if, label %join
>   
>   if: 
>     %cmp1 = icmp sgt i32 %x, 1
>     %cmp2 = icmp sgt i32 %x, 0
>     br i1 %cmp1, label %join, label %exit
>   
>   join:
>     %phi = phi i1 [ %cmp2, %if ], [ false, %entry ]
>     ret i1 %phi
>   
>   exit:
>     ret i1 false
>   }
>
> Here the fact is known only along the edge, but in neither of the blocks. I don't expect this to actually get folded...

Yep, if the fact is only known on the edge then we don't simplify it at the moment. This could probably be handled by making the fact handling more fine-grained.

I *think* this should already be covered by the following test. It's a 3 entry phi, not sure if it is worth adding a dedicated simpler case? https://github.com/llvm/llvm-project/blob/main/llvm/test/Transforms/ConstraintElimination/cond-used-in-phi.ll#L221


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D153660/new/

https://reviews.llvm.org/D153660

Files:
  llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
  llvm/test/Transforms/ConstraintElimination/and-implied-by-operands.ll
  llvm/test/Transforms/ConstraintElimination/assumes.ll
  llvm/test/Transforms/ConstraintElimination/cond-used-in-phi.ll
  llvm/test/Transforms/ConstraintElimination/monotonic-pointer-phis-crashes.ll
  llvm/test/Transforms/ConstraintElimination/uses-in-different-blocks.ll

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