[llvm] [KnownBits] Implement knownbits lshr/ashr with exact flag (PR #84254)

[via llvm-commits]

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@@ -320,6 +320,22 @@ TEST(KnownBitsTest, AbsDiffSpecialCase) {
   EXPECT_EQ(0b0000ul, Res.Zero.getZExtValue());
 }
 
+TEST(KnownBitsTest, ShrExactSpecialCase) {
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goldsteinn wrote:

This was just to show a case where exact provides info that non-exact doesn't. But ill change this to an IR test where the codegen actually varies @dtcxzyw's request.

https://github.com/llvm/llvm-project/pull/84254