diff options
Diffstat (limited to 'llvm')
| -rw-r--r-- | llvm/lib/Analysis/ValueTracking.cpp | 3 | ||||
| -rw-r--r-- | llvm/test/Transforms/InstCombine/shift.ll | 10 |
2 files changed, 12 insertions, 1 deletions
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp index 7cb8c8d8aae..b065f427b06 100644 --- a/llvm/lib/Analysis/ValueTracking.cpp +++ b/llvm/lib/Analysis/ValueTracking.cpp @@ -852,7 +852,8 @@ static void computeKnownBitsFromShiftOperator( Optional<bool> ShifterOperandIsNonZero; // Early exit if we can't constrain any well-defined shift amount. - if (!(ShiftAmtKZ & (BitWidth - 1)) && !(ShiftAmtKO & (BitWidth - 1))) { + if (!(ShiftAmtKZ & (PowerOf2Ceil(BitWidth) - 1)) && + !(ShiftAmtKO & (PowerOf2Ceil(BitWidth) - 1))) { ShifterOperandIsNonZero = isKnownNonZero(I->getOperand(1), Depth + 1, Q); if (!*ShifterOperandIsNonZero) diff --git a/llvm/test/Transforms/InstCombine/shift.ll b/llvm/test/Transforms/InstCombine/shift.ll index ce8e2fcd38b..68bbf35d1e6 100644 --- a/llvm/test/Transforms/InstCombine/shift.ll +++ b/llvm/test/Transforms/InstCombine/shift.ll @@ -1306,3 +1306,13 @@ define <2 x i8> @lshr_demanded_bits_splat(<2 x i8> %x) { ret <2 x i8> %shr } +; Make sure known bits works correctly with non power of 2 bit widths. +define i7 @test65(i7 %a, i7 %b) { +; CHECK-LABEL: @test65( +; CHECK-NEXT: ret i7 0 +; + %shiftamt = and i7 %b, 6 ; this ensures the shift amount is even and less than the bit width. + %x = lshr i7 42, %shiftamt ; 42 has a zero in every even numbered bit and a one in every odd bit. + %y = and i7 %x, 1 ; this extracts the lsb which should be 0 because we shifted an even number of bits and all even bits of the shift input are 0. + ret i7 %y +} |
