[PATCH] D34165: [ValueTracking] Correct early out in computeKnownBitsFromOperator to work with non power of 2 bit widths
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Wed Jun 14 10:05:37 PDT 2017
This revision was automatically updated to reflect the committed changes.
Closed by commit rL305400: [ValueTracking] Correct early out in computeKnownBitsFromOperator to work with… (authored by ctopper).
Changed prior to commit:
https://reviews.llvm.org/D34165?vs=102490&id=102567#toc
Repository:
rL LLVM
https://reviews.llvm.org/D34165
Files:
llvm/trunk/lib/Analysis/ValueTracking.cpp
llvm/trunk/test/Transforms/InstCombine/shift.ll
Index: llvm/trunk/test/Transforms/InstCombine/shift.ll
===================================================================
--- llvm/trunk/test/Transforms/InstCombine/shift.ll
+++ llvm/trunk/test/Transforms/InstCombine/shift.ll
@@ -1306,3 +1306,13 @@
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
+}
Index: llvm/trunk/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp
@@ -852,7 +852,8 @@
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)
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