[PATCH] D34165: [ValueTracking] Correct early out in computeKnownBitsFromOperator to work with non power of 2 bit widths

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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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