[PATCH] D137934: [InstCombine] Fold extractelt with select of constants

[Jay Foad via Phabricator via llvm-commits]

foad accepted this revision.
foad added a comment.
This revision is now accepted and ready to land.

The code LGTM.



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Comment at: llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp:401-402
 
+  // extractelt (select %x, <vec1>, <vec2>), %const ->
+  // select %x, <vec1>[%const], <vec2>[%const]
+  // FIXME: Support multiple select operands during constant folding:
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Why do you write `<vec1>` instead of `%vec1`? I found it confusing to have two different syntaxes for variables in the same line.


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Comment at: llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp:403-406
+  // FIXME: Support multiple select operands during constant folding:
+  // extractelt (select %c, %<vec1>, %<vec2>), (select %c, %c1, %c2)
+  // This is currently not possible because constant folding will reach
+  // an unreachable assertion if it doesn't find a constant operand.
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I don't really understand this comment. "FIXME" suggests that something is broken. What is broken? What would you like to fold `extractelt (select %c, %<vec1>, %<vec2>), (select %c, %c1, %c2)` into?


Repository:
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  https://reviews.llvm.org/D137934/new/

https://reviews.llvm.org/D137934