[ConstraintElimination] Support constraints with only const ops.

Remove the early exit if both constraints contain no variables. This
restriction is unnecessayr for correctness and removing it simplifies
handling of trivial constant conditions in follow-up changes.

diff --git a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
index a2b62fb..7c6d696 100644 (file)
--- a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
@@ -282,10 +282,6 @@ getConstraint(CmpInst::Predicate Pred, Value *Op0, Value *Op1,
   if (ADec.empty() || BDec.empty())
     return {};
 
-  // Skip trivial constraints without any variables.
-  if (ADec.size() == 1 && BDec.size() == 1)
-    return {};
-
   int64_t Offset1 = ADec[0].first;
   int64_t Offset2 = BDec[0].first;
   Offset1 *= -1;
@@ -350,7 +346,7 @@ bool ConstraintTy::isValid(const ConstraintInfo &Info) const {
                Info.getValue2Index(CmpInst::isSigned(C.Pred)), NewIndices);
            // TODO: properly check NewIndices.
            return NewIndices.empty() && R.Preconditions.empty() && !R.IsEq &&
-                  R.size() >= 2 &&
+                  R.size() >= 1 &&
                   Info.getCS(CmpInst::isSigned(C.Pred))
                       .isConditionImplied(R.Coefficients);
          });
@@ -631,7 +627,7 @@ static bool eliminateConstraints(Function &F, DominatorTree &DT) {
 
         DenseMap<Value *, unsigned> NewIndices;
         auto R = getConstraint(Cmp, Info, NewIndices);
-        if (R.IsEq || R.size() < 2 || R.needsNewIndices(NewIndices) ||
+        if (R.IsEq || R.empty() || R.needsNewIndices(NewIndices) ||
             !R.isValid(Info))
           continue;
 

diff --git a/llvm/test/Transforms/ConstraintElimination/constants.ll b/llvm/test/Transforms/ConstraintElimination/constants.ll
index eeb8124..896eb07 100644 (file)
--- a/llvm/test/Transforms/ConstraintElimination/constants.ll
+++ b/llvm/test/Transforms/ConstraintElimination/constants.ll
@@ -6,11 +6,11 @@ define i1 @test_ult() {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[T_0:%.*]] = icmp ult i8 10, 11
 ; CHECK-NEXT:    [[F_0:%.*]] = icmp ult i8 10, 10
-; CHECK-NEXT:    [[RES_1:%.*]] = xor i1 [[T_0]], [[F_0]]
+; CHECK-NEXT:    [[RES_1:%.*]] = xor i1 true, false
 ; CHECK-NEXT:    [[F_1:%.*]] = icmp ult i8 10, 9
-; CHECK-NEXT:    [[RES_2:%.*]] = xor i1 [[RES_1]], [[F_1]]
+; CHECK-NEXT:    [[RES_2:%.*]] = xor i1 [[RES_1]], false
 ; CHECK-NEXT:    [[T_1:%.*]] = icmp ult i8 10, -10
-; CHECK-NEXT:    [[RES_3:%.*]] = xor i1 [[RES_2]], [[T_1]]
+; CHECK-NEXT:    [[RES_3:%.*]] = xor i1 [[RES_2]], true
 ; CHECK-NEXT:    ret i1 [[RES_3]]
 ;
 entry:
@@ -75,11 +75,11 @@ define i1 @test_slt() {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[T_0:%.*]] = icmp ult i8 10, 11
 ; CHECK-NEXT:    [[F_0:%.*]] = icmp ult i8 10, 10
-; CHECK-NEXT:    [[RES_1:%.*]] = xor i1 [[T_0]], [[F_0]]
+; CHECK-NEXT:    [[RES_1:%.*]] = xor i1 true, false
 ; CHECK-NEXT:    [[F_1:%.*]] = icmp ult i8 10, 9
-; CHECK-NEXT:    [[RES_2:%.*]] = xor i1 [[RES_1]], [[F_1]]
+; CHECK-NEXT:    [[RES_2:%.*]] = xor i1 [[RES_1]], false
 ; CHECK-NEXT:    [[F_2:%.*]] = icmp ult i8 10, -10
-; CHECK-NEXT:    [[RES_3:%.*]] = xor i1 [[RES_2]], [[F_2]]
+; CHECK-NEXT:    [[RES_3:%.*]] = xor i1 [[RES_2]], true
 ; CHECK-NEXT:    ret i1 [[RES_3]]
 ;
 entry: