return getICmp(I.ICMP_EQ, A, ConstantInt::getNullValue(A->getType()));
}
+ bool IsNegative = false;
if (IsAShr) {
if (AP1.isNegative() != AP2.isNegative()) {
// Arithmetic shift will never change the sign.
return getConstant(false);
}
- // Both the constants are negative, take their positive to calculate
- // log.
+ // Both the constants are negative, take their positive to calculate log.
if (AP1.isNegative()) {
- AP1 = -AP1;
- AP2 = -AP2;
+ if (AP1.slt(AP2))
+ // Right-shifting won't increase the magnitude.
+ return getConstant(false);
+ IsNegative = true;
}
}
- if (AP1.ugt(AP2)) {
+ if (!IsNegative && AP1.ugt(AP2))
// Right-shifting will not increase the value.
return getConstant(false);
- }
// Get the distance between the highest bit that's set.
- int Shift = AP2.logBase2() - AP1.logBase2();
+ int Shift;
+ if (IsNegative)
+ Shift = (-AP2).logBase2() - (-AP1).logBase2();
+ else
+ Shift = AP2.logBase2() - AP1.logBase2();
- // Use lshr here, since we've canonicalized to +ve numbers.
- if (AP1 == AP2.lshr(Shift))
+ if (IsAShr ? AP1 == AP2.ashr(Shift) : AP1 == AP2.lshr(Shift))
return getICmp(I.ICMP_EQ, A, ConstantInt::get(A->getType(), Shift));
// Shifting const2 will never be equal to const1.
%cmp = icmp ne i8 %shr, -30
ret i1 %cmp
}
+
+; Don't try to fold the entire body of function @PR20945 into a
+; single `ret i1 true` statement.
+; If %B is equal to 1, then this function would return false.
+; As a consequence, the instruction combiner is not allowed to fold %cmp
+; to 'true'. Instead, it should replace %cmp with a simpler comparison
+; between %B and 1.
+
+; CHECK-LABEL: @PR20945(
+; CHECK: icmp ne i32 %B, 1
+define i1 @PR20945(i32 %B) {
+ %shr = ashr i32 -9, %B
+ %cmp = icmp ne i32 %shr, -5
+ ret i1 %cmp
+}