computeKnownBits(I->getOperand(1), KnownZero, KnownOne, Depth + 1, Q);
+ // If the shift amount could be greater than or equal to the bit-width of the LHS, the
+ // value could be undef, so we don't know anything about it.
+ if ((~KnownZero).uge(BitWidth)) {
+ KnownZero.clearAllBits();
+ KnownOne.clearAllBits();
+ return;
+ }
+
// Note: We cannot use KnownZero.getLimitedValue() here, because if
// BitWidth > 64 and any upper bits are known, we'll end up returning the
// limit value (which implies all bits are known).
; CHECK-NEXT: ret i8 %zext
}
+; Here, widening the or from i1 to i32 and removing one of the icmps would
+; widen an undef value (created by the out-of-range shift), increasing the
+; range of valid values for the return, so we can't do it.
+define i32 @dont_widen_undef() {
+entry:
+ br label %block2
+
+block1:
+ br label %block2
+
+block2:
+ %m.011 = phi i32 [ 33, %entry ], [ 0, %block1 ]
+ %cmp.i = icmp ugt i32 %m.011, 1
+ %m.1.op = lshr i32 1, %m.011
+ %sext.mask = and i32 %m.1.op, 65535
+ %cmp115 = icmp ne i32 %sext.mask, 0
+ %cmp1 = or i1 %cmp.i, %cmp115
+ %conv2 = zext i1 %cmp1 to i32
+ ret i32 %conv2
+
+; CHECK-LABEL: dont_widen_undef(
+; CHECK: %m.011 = phi i32 [ 33, %entry ], [ 0, %block1 ]
+; CHECK-NEXT: %cmp.i = icmp ugt i32 %m.011, 1
+; CHECK-NEXT: %m.1.op = lshr i32 1, %m.011
+; CHECK-NEXT: %sext.mask = and i32 %m.1.op, 65535
+; CHECK-NEXT: %cmp115 = icmp ne i32 %sext.mask, 0
+; CHECK-NEXT: %cmp1 = or i1 %cmp.i, %cmp115
+; CHECK-NEXT: %conv2 = zext i1 %cmp1 to i32
+; CHECK-NEXT: ret i32 %conv2
+}