[InstSimplify] Check common operand with constant earlier

If both icmps have the same operands and the RHS is constant, we
would currently go into the isImpliedCondMatchingOperands() code
path, instead of the isImpliedCondCommonOperandWithConstants()
path. Both are correct, but the latter can produce more accurate
results if the implication is dependent on the sign.

Author: nikic

llvm/lib/Analysis/ValueTracking.cpp

@@ -8352,17 +8352,17 @@ static std::optional<bool> isImpliedCondICmps(const ICmpInst *LHS,
   CmpInst::Predicate LPred =
       LHSIsTrue ? LHS->getPredicate() : LHS->getInversePredicate();
 
-  // Can we infer anything when the two compares have matching operands?
-  bool AreSwappedOps;
-  if (areMatchingOperands(L0, L1, R0, R1, AreSwappedOps))
-    return isImpliedCondMatchingOperands(LPred, RPred, AreSwappedOps);
-
   // Can we infer anything when the 0-operands match and the 1-operands are
   // constants (not necessarily matching)?
   const APInt *LC, *RC;
   if (L0 == R0 && match(L1, m_APInt(LC)) && match(R1, m_APInt(RC)))
     return isImpliedCondCommonOperandWithConstants(LPred, *LC, RPred, *RC);
 
+  // Can we infer anything when the two compares have matching operands?
+  bool AreSwappedOps;
+  if (areMatchingOperands(L0, L1, R0, R1, AreSwappedOps))
+    return isImpliedCondMatchingOperands(LPred, RPred, AreSwappedOps);
+
   // L0 = R0 = L1 + R1, L0 >=u L1 implies R0 >=u R1, L0 <u L1 implies R0 <u R1
   if (ICmpInst::isUnsigned(LPred) && ICmpInst::isUnsigned(RPred)) {
     if (L0 == R1) {

llvm/test/Transforms/InstSimplify/implies.ll

@@ -501,10 +501,7 @@ define i1 @lshr_value(i32 %length.i, i32 %i, i32 %v) {
 
 define i1 @same_ops_with_constant(i8 %x) {
 ; CHECK-LABEL: @same_ops_with_constant(
-; CHECK-NEXT:    [[CMP1:%.*]] = icmp sgt i8 [[X:%.*]], 5
-; CHECK-NEXT:    [[CMP2:%.*]] = icmp ugt i8 [[X]], 5
-; CHECK-NEXT:    [[RES:%.*]] = icmp ule i1 [[CMP1]], [[CMP2]]
-; CHECK-NEXT:    ret i1 [[RES]]
+; CHECK-NEXT:    ret i1 true
 ;
   %cmp1 = icmp sgt i8 %x, 5
   %cmp2 = icmp ugt i8 %x, 5