Index: lib/Transforms/InstCombine/InstCombineCasts.cpp =================================================================== --- lib/Transforms/InstCombine/InstCombineCasts.cpp +++ lib/Transforms/InstCombine/InstCombineCasts.cpp @@ -950,8 +950,13 @@ unsigned VSize = V->getType()->getScalarSizeInBits(); if (IC.MaskedValueIsZero(I->getOperand(1), APInt::getHighBitsSet(VSize, BitsToClear), - 0, CxtI)) + 0, CxtI)) { + // If this is an And instruction and all of the BitsToClear are + // known to be zero we can reset BitsToClear. + if (Opc == Instruction::And) + BitsToClear = 0; return true; + } } // Otherwise, we don't know how to analyze this BitsToClear case yet. Index: test/Transforms/InstCombine/cast.ll =================================================================== --- test/Transforms/InstCombine/cast.ll +++ test/Transforms/InstCombine/cast.ll @@ -1588,15 +1588,12 @@ } ; We should be able to remove the zext and trunc here. -; TODO: This is currently blocked because we don't realize the 'and' has cleared the extra bits that would be shifted in widening the lshr. define i32 @test95(i32 %x) { ; CHECK-LABEL: @test95( -; 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]] +; CHECK-NEXT: [[TMP1:%.*]] = lshr i32 [[X:%.*]], 6 +; CHECK-NEXT: [[TMP2:%.*]] = and i32 [[TMP1]], 2 +; CHECK-NEXT: [[TMP3:%.*]] = or i32 [[TMP2]], 40 +; CHECK-NEXT: ret i32 [[TMP3]] ; %1 = trunc i32 %x to i8 %2 = lshr i8 %1, 6