[PATCH] D36498: [InstCombine] Teach foldSelectICmpAnd to recognize a (icmp slt trunc X, 0) and (icmp sgt trunc X, -1) as equivalent to an and with the sign bit of the truncated type

[Sanjay Patel via Phabricator via llvm-commits]

spatel added inline comments.


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Comment at: test/Transforms/InstCombine/select-with-bitwise-ops.ll:425-431
+; CHECK-LABEL: @test72(
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc i32 [[X:%.*]] to i8
+; CHECK-NEXT:    [[TMP2:%.*]] = lshr i8 [[TMP1]], 6
+; CHECK-NEXT:    [[TMP3:%.*]] = and i8 [[TMP2]], 2
+; CHECK-NEXT:    [[TMP4:%.*]] = or i8 [[TMP3]], 40
+; CHECK-NEXT:    [[TMP5:%.*]] = zext i8 [[TMP4]] to i32
+; CHECK-NEXT:    ret i32 [[TMP5]]
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Sorry if I missed it, but do you know why canEvaluateZExtd() failed on this?
If you have a fix, I'd rather see that go in first because this doesn't look better in IR or x86 codegen.


https://reviews.llvm.org/D36498