[InstCombine] Fix regressions from canonicalizing (icmp eq/ne (X, Y), Y -> (icmp eq/ne (~X, Y), 0)

This issue is the canonicalization can consume `not` instruction which
are a limitted resource and are use to enable multiple transforms.

In this case `foldICmpWithLowBitMaskedVal` is a "better" user of `not`
instructions, so just check if that has a result first.

Author: goldsteinn

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

@@ -4734,6 +4734,11 @@ static Instruction *foldICmpAndXX(ICmpInst &I, const SimplifyQuery &Q,
         return new ICmpInst(Pred, IC.Builder.CreateOr(A, NotOp1),
                             Constant::getAllOnesValue(Op1->getType()));
     // icmp (X & Y) eq/ne Y --> (~X & Y) eq/ne 0 if X  is freely invertible.
+    // Since we may be consuming a `not` here, first check if we match
+    // `foldICmpWithLowBitMaskedVal` as it is a "better" user of `not`
+    // instructions.
+    if (Value *R = foldICmpWithLowBitMaskedVal(Pred, Op0, Op1, Q, IC))
+      return IC.replaceInstUsesWith(I, R);
     if (auto *NotA = IC.getFreelyInverted(A, A->hasOneUse(), &IC.Builder))
       return new ICmpInst(Pred, IC.Builder.CreateAnd(Op1, NotA),
                           Constant::getNullValue(Op1->getType()));

llvm/test/Transforms/InstCombine/canonicalize-low-bit-mask-v2-and-icmp-eq-to-icmp-ule.ll

@@ -144,7 +144,7 @@ define i1 @oneuse0(i8 %x, i8 %y) {
 ; CHECK-LABEL: @oneuse0(
 ; CHECK-NEXT:    [[T0:%.*]] = shl nsw i8 -1, [[Y:%.*]]
 ; CHECK-NEXT:    call void @use8(i8 [[T0]])
-; CHECK-NEXT:    [[X_HIGHBITS:%.*]] = and i8 [[T0]], [[X:%.*]]
+; CHECK-NEXT:    [[X_HIGHBITS:%.*]] = lshr i8 [[X:%.*]], [[Y]]
 ; CHECK-NEXT:    [[RET:%.*]] = icmp eq i8 [[X_HIGHBITS]], 0
 ; CHECK-NEXT:    ret i1 [[RET]]
 ;
@@ -161,8 +161,7 @@ define i1 @oneuse1(i8 %x, i8 %y) {
 ; CHECK-NEXT:    [[T0:%.*]] = shl nsw i8 -1, [[Y:%.*]]
 ; CHECK-NEXT:    [[T1:%.*]] = xor i8 [[T0]], -1
 ; CHECK-NEXT:    call void @use8(i8 [[T1]])
-; CHECK-NEXT:    [[TMP1:%.*]] = and i8 [[T0]], [[X:%.*]]
-; CHECK-NEXT:    [[RET:%.*]] = icmp eq i8 [[TMP1]], 0
+; CHECK-NEXT:    [[RET:%.*]] = icmp uge i8 [[T1]], [[X:%.*]]
 ; CHECK-NEXT:    ret i1 [[RET]]
 ;
   %t0 = shl i8 -1, %y
@@ -196,8 +195,7 @@ define i1 @oneuse3(i8 %x, i8 %y) {
 ; CHECK-NEXT:    call void @use8(i8 [[T0]])
 ; CHECK-NEXT:    [[T1:%.*]] = xor i8 [[T0]], -1
 ; CHECK-NEXT:    call void @use8(i8 [[T1]])
-; CHECK-NEXT:    [[TMP1:%.*]] = and i8 [[T0]], [[X:%.*]]
-; CHECK-NEXT:    [[RET:%.*]] = icmp eq i8 [[TMP1]], 0
+; CHECK-NEXT:    [[RET:%.*]] = icmp uge i8 [[T1]], [[X:%.*]]
 ; CHECK-NEXT:    ret i1 [[RET]]
 ;
   %t0 = shl i8 -1, %y

llvm/test/Transforms/InstCombine/canonicalize-low-bit-mask-v2-and-icmp-ne-to-icmp-ugt.ll

@@ -144,7 +144,7 @@ define i1 @oneuse0(i8 %x, i8 %y) {
 ; CHECK-LABEL: @oneuse0(
 ; CHECK-NEXT:    [[T0:%.*]] = shl nsw i8 -1, [[Y:%.*]]
 ; CHECK-NEXT:    call void @use8(i8 [[T0]])
-; CHECK-NEXT:    [[X_HIGHBITS:%.*]] = and i8 [[T0]], [[X:%.*]]
+; CHECK-NEXT:    [[X_HIGHBITS:%.*]] = lshr i8 [[X:%.*]], [[Y]]
 ; CHECK-NEXT:    [[RET:%.*]] = icmp ne i8 [[X_HIGHBITS]], 0
 ; CHECK-NEXT:    ret i1 [[RET]]
 ;
@@ -161,8 +161,7 @@ define i1 @oneuse1(i8 %x, i8 %y) {
 ; CHECK-NEXT:    [[T0:%.*]] = shl nsw i8 -1, [[Y:%.*]]
 ; CHECK-NEXT:    [[T1:%.*]] = xor i8 [[T0]], -1
 ; CHECK-NEXT:    call void @use8(i8 [[T1]])
-; CHECK-NEXT:    [[TMP1:%.*]] = and i8 [[T0]], [[X:%.*]]
-; CHECK-NEXT:    [[RET:%.*]] = icmp ne i8 [[TMP1]], 0
+; CHECK-NEXT:    [[RET:%.*]] = icmp ult i8 [[T1]], [[X:%.*]]
 ; CHECK-NEXT:    ret i1 [[RET]]
 ;
   %t0 = shl i8 -1, %y
@@ -196,8 +195,7 @@ define i1 @oneuse3(i8 %x, i8 %y) {
 ; CHECK-NEXT:    call void @use8(i8 [[T0]])
 ; CHECK-NEXT:    [[T1:%.*]] = xor i8 [[T0]], -1
 ; CHECK-NEXT:    call void @use8(i8 [[T1]])
-; CHECK-NEXT:    [[TMP1:%.*]] = and i8 [[T0]], [[X:%.*]]
-; CHECK-NEXT:    [[RET:%.*]] = icmp ne i8 [[TMP1]], 0
+; CHECK-NEXT:    [[RET:%.*]] = icmp ult i8 [[T1]], [[X:%.*]]
 ; CHECK-NEXT:    ret i1 [[RET]]
 ;
   %t0 = shl i8 -1, %y