[ConstraintElimination] Add function arguments to constraint system before solving

If there is an optimisation opportunity and the function argument hasn’t been added to constraint
system through previous facts we fail to optimise it.

It might be a good idea to start the constraint system with all the function arguments added to the system

Reviewed By: fhahn

Differential Revision: https://reviews.llvm.org/D144879

Author: Zain Jaffal

llvm/include/llvm/Analysis/ConstraintSystem.h

@@ -19,7 +19,6 @@
 namespace llvm {
 
 class Value;
-
 class ConstraintSystem {
   struct Entry {
     int64_t Coefficient;
@@ -68,8 +67,14 @@ class ConstraintSystem {
 
 public:
   ConstraintSystem() {}
+  ConstraintSystem(ArrayRef<Value *> FunctionArgs) {
+    NumVariables += FunctionArgs.size();
+    for (auto *Arg : FunctionArgs) {
+      Value2Index.insert({Arg, Value2Index.size() + 1});
+    }
+  }
   ConstraintSystem(const DenseMap<Value *, unsigned> &Value2Index)
-      : Value2Index(Value2Index) {}
+      : NumVariables(Value2Index.size()), Value2Index(Value2Index) {}
 
   bool addVariableRow(ArrayRef<int64_t> R) {
     assert(Constraints.empty() || R.size() == NumVariables);

llvm/lib/Transforms/Scalar/ConstraintElimination.cpp

@@ -139,7 +139,8 @@ class ConstraintInfo {
   const DataLayout &DL;
 
 public:
-  ConstraintInfo(const DataLayout &DL) : DL(DL) {}
+  ConstraintInfo(const DataLayout &DL, ArrayRef<Value *> FunctionArgs)
+      : UnsignedCS(FunctionArgs), SignedCS(FunctionArgs), DL(DL) {}
 
   DenseMap<Value *, unsigned> &getValue2Index(bool Signed) {
     return Signed ? SignedCS.getValue2Index() : UnsignedCS.getValue2Index();
@@ -1087,8 +1088,10 @@ static bool eliminateConstraints(Function &F, DominatorTree &DT,
                                  OptimizationRemarkEmitter &ORE) {
   bool Changed = false;
   DT.updateDFSNumbers();
-
-  ConstraintInfo Info(F.getParent()->getDataLayout());
+  SmallVector<Value *> FunctionArgs;
+  for (Value &Arg : F.args())
+    FunctionArgs.push_back(&Arg);
+  ConstraintInfo Info(F.getParent()->getDataLayout(), FunctionArgs);
   State S(DT);
   std::unique_ptr<Module> ReproducerModule(
       DumpReproducers ? new Module(F.getName(), F.getContext()) : nullptr);

llvm/test/Transforms/ConstraintElimination/transfer-signed-facts-to-unsigned.ll

@@ -295,8 +295,6 @@ else:
   ret i1 1
 }
 
-; TODO: Even though %cnt is not known signed positive %cmp can be simplified
-; because %add.ptr uses it zero-extended.
 define i1 @cnt_not_known_positive_sgt_against_base_with_zext(ptr %p, i32 %cnt) {
 ; CHECK-LABEL: @cnt_not_known_positive_sgt_against_base_with_zext(
 ; CHECK-NEXT:  entry:
@@ -305,7 +303,7 @@ define i1 @cnt_not_known_positive_sgt_against_base_with_zext(ptr %p, i32 %cnt) {
 ; CHECK-NEXT:    [[EXT:%.*]] = zext i32 [[CNT]] to i64
 ; CHECK-NEXT:    [[ADD_PTR:%.*]] = getelementptr inbounds i32, ptr [[P:%.*]], i64 [[EXT]]
 ; CHECK-NEXT:    [[CMP_1:%.*]] = icmp uge ptr [[ADD_PTR]], [[P]]
-; CHECK-NEXT:    br i1 [[CMP_1]], label [[THEN:%.*]], label [[ELSE:%.*]]
+; CHECK-NEXT:    br i1 true, label [[THEN:%.*]], label [[ELSE:%.*]]
 ; CHECK:       then:
 ; CHECK-NEXT:    ret i1 false
 ; CHECK:       else:
@@ -326,8 +324,6 @@ else:
   ret i1 1
 }
 
-; TODO: Even though %cnt is not known signed positive %cmp can be simplified
-; because %add.ptr uses it zero-extended.
 define i1 @cnt_not_known_positive_sge_against_base_with_zext(ptr %p, i32 %cnt) {
 ; CHECK-LABEL: @cnt_not_known_positive_sge_against_base_with_zext(
 ; CHECK-NEXT:  entry:
@@ -336,7 +332,7 @@ define i1 @cnt_not_known_positive_sge_against_base_with_zext(ptr %p, i32 %cnt) {
 ; CHECK-NEXT:    [[EXT:%.*]] = zext i32 [[CNT]] to i64
 ; CHECK-NEXT:    [[ADD_PTR:%.*]] = getelementptr inbounds i32, ptr [[P:%.*]], i64 [[EXT]]
 ; CHECK-NEXT:    [[CMP_1:%.*]] = icmp uge ptr [[ADD_PTR]], [[P]]
-; CHECK-NEXT:    br i1 [[CMP_1]], label [[THEN:%.*]], label [[ELSE:%.*]]
+; CHECK-NEXT:    br i1 true, label [[THEN:%.*]], label [[ELSE:%.*]]
 ; CHECK:       then:
 ; CHECK-NEXT:    ret i1 false
 ; CHECK:       else:
@@ -453,7 +449,6 @@ else:
   ret i1 1
 }
 
-; TODO: Even though %cnt is not known signed positive %cmp can be simplified
 ; because %add.ptr uses it zero-extended.
 define i1 @cnt_not_known_positive_from_branch_check_against_base_struct_ugt_with_zext(ptr %p, i32 %cnt) {
 ; CHECK-LABEL: @cnt_not_known_positive_from_branch_check_against_base_struct_ugt_with_zext(
@@ -464,7 +459,7 @@ define i1 @cnt_not_known_positive_from_branch_check_against_base_struct_ugt_with
 ; CHECK-NEXT:    [[EXT:%.*]] = zext i32 [[CNT]] to i64
 ; CHECK-NEXT:    [[GEP_EXT:%.*]] = getelementptr inbounds [[T:%.*]], ptr [[P:%.*]], i64 0, i32 1, i64 [[EXT]]
 ; CHECK-NEXT:    [[CMP_1:%.*]] = icmp ugt ptr [[GEP_EXT]], [[P]]
-; CHECK-NEXT:    br i1 [[CMP_1]], label [[THEN:%.*]], label [[ELSE]]
+; CHECK-NEXT:    br i1 true, label [[THEN:%.*]], label [[ELSE]]
 ; CHECK:       then:
 ; CHECK-NEXT:    ret i1 false
 ; CHECK:       else: