[InstCombine] [NFC] use C.isNegatedPowerOf2() instead of (~C + 1).isPowerOf2()

[RKSimon]

LGTM - although its probably best that the test is committed separately as its not dependent on the NFC code change.

[Chenbing.Zheng]

In D129103#3629390, @RKSimon wrote:

LGTM - although its probably best that the test is committed separately as its not dependent on the NFC code change.

OK，I will separate it when I commit.

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

if (Cmp.isEquality() && C1.isZero()) {
     if (C2->isSignMask()) {
       Constant *Zero = Constant::getNullValue(X->getType());
       auto NewPred = isICMP_NE ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_SGE;
       return new ICmpInst(NewPred, X, Zero);
     }
 
     // Restrict this fold only for single-use 'and' (PR10267).
     // ((%x & C) == 0) --> %x u< (-C)  iff (-C) is power of two.
-    if ((~(*C2) + 1).isPowerOf2()) {
+    if (C2->isNegatedPowerOf2()) {
       Constant *NegBOC =
           ConstantExpr::getNeg(cast<Constant>(And->getOperand(1)));
       auto NewPred = isICMP_NE ? ICmpInst::ICMP_UGE : ICmpInst::ICMP_ULT;
       return new ICmpInst(NewPred, X, NegBOC);
     }
   }
 
   // If the LHS is an 'and' of a truncate and we can widen the and/compare to

llvm/test/Transforms/InstCombine/lshr-and-negC-icmpeq-zero.ll

 ; CHECK-LABEL: @scalar_i32_lshr_and_negC_eq_nonzero(
 ; CHECK-NEXT:    ret i1 false
 ;
   %lshr = lshr i32 %x, %y
   %and = and i32 %lshr, 4294967288  ; ~7
   %r = icmp eq i32 %and, 1  ; should be comparing with 0
   ret i1 %r
 }
+
+; Not NegatedPowerOf2
+
+define i1 @scalar_i8_lshr_and_negC_eq_not_negatedPowerOf2(i8 %x, i8 %y) {
+; CHECK-LABEL: @scalar_i8_lshr_and_negC_eq_not_negatedPowerOf2(
+; CHECK-NEXT:    [[TMP1:%.*]] = shl i8 -3, [[Y:%.*]]
+; CHECK-NEXT:    [[TMP2:%.*]] = and i8 [[TMP1]], [[X:%.*]]
+; CHECK-NEXT:    [[R:%.*]] = icmp eq i8 [[TMP2]], 0
+; CHECK-NEXT:    ret i1 [[R]]
+;
+  %lshr = lshr i8 %x, %y
+  %and = and i8 %lshr, 253  ; -3
+  %r = icmp eq i8 %and, 0
+  ret i1 %r
+}