[llvm] [KnownBits] Check that mul is optimal for low order bits (PR #113316)

[Jay Foad via llvm-commits]

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@@ -815,4 +815,38 @@ TEST(KnownBitsTest, ConcatBits) {
   }
 }
 
+TEST(KnownBitsTest, MulExhaustive) {
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jayfoad wrote:

I don't think the current name is wrong, and I hope to extend it to high bits as well as low bits.

https://github.com/llvm/llvm-project/pull/113316