[CmpInstAnalysis] Further canonicalize the predicate (NFC)

Canonicalize le to lt predicate by adjusting the constant by one.
As such, we only have to handle slt and ult.

This will make it easier to handle additional cases.

Author: nikic

llvm/lib/Analysis/CmpInstAnalysis.cpp

@@ -78,8 +78,8 @@ llvm::decomposeBitTestICmp(Value *LHS, Value *RHS, CmpInst::Predicate Pred,
                            bool LookThruTrunc) {
   using namespace PatternMatch;
 
-  const APInt *C;
-  if (!ICmpInst::isRelational(Pred) || !match(RHS, m_APIntAllowPoison(C)))
+  const APInt *OrigC;
+  if (!ICmpInst::isRelational(Pred) || !match(RHS, m_APIntAllowPoison(OrigC)))
     return std::nullopt;
 
   bool Inverted = false;
@@ -88,36 +88,30 @@ llvm::decomposeBitTestICmp(Value *LHS, Value *RHS, CmpInst::Predicate Pred,
     Pred = ICmpInst::getInversePredicate(Pred);
   }
 
+  APInt C = *OrigC;
+  if (ICmpInst::isLE(Pred)) {
+    if (ICmpInst::isSigned(Pred) ? C.isMaxSignedValue() : C.isMaxValue())
+      return std::nullopt;
+    ++C;
+    Pred = ICmpInst::getStrictPredicate(Pred);
+  }
+
   DecomposedBitTest Result;
   switch (Pred) {
   default:
     llvm_unreachable("Unexpected predicate");
   case ICmpInst::ICMP_SLT:
     // X < 0 is equivalent to (X & SignMask) != 0.
-    if (!C->isZero())
+    if (!C.isZero())
       return std::nullopt;
-    Result.Mask = APInt::getSignMask(C->getBitWidth());
-    Result.Pred = ICmpInst::ICMP_NE;
-    break;
-  case ICmpInst::ICMP_SLE:
-    // X <= -1 is equivalent to (X & SignMask) != 0.
-    if (!C->isAllOnes())
-      return std::nullopt;
-    Result.Mask = APInt::getSignMask(C->getBitWidth());
+    Result.Mask = APInt::getSignMask(C.getBitWidth());
     Result.Pred = ICmpInst::ICMP_NE;
     break;
   case ICmpInst::ICMP_ULT:
     // X <u 2^n is equivalent to (X & ~(2^n-1)) == 0.
-    if (!C->isPowerOf2())
-      return std::nullopt;
-    Result.Mask = -*C;
-    Result.Pred = ICmpInst::ICMP_EQ;
-    break;
-  case ICmpInst::ICMP_ULE:
-    // X <=u 2^n-1 is equivalent to (X & ~(2^n-1)) == 0.
-    if (!(*C + 1).isPowerOf2())
+    if (!C.isPowerOf2())
       return std::nullopt;
-    Result.Mask = ~*C;
+    Result.Mask = -C;
     Result.Pred = ICmpInst::ICMP_EQ;
     break;
   }