Add support for constant folding of clamp()

src/OpenGL/compiler/ParseHelper.cpp

@@ -3629,6 +3629,29 @@ TIntermTyped *TParseContext::addFunctionCallOrMethod(TFunction *fnCall, TIntermN
 
 					callNode = aggregate;
 
+					if(op == EOpClamp)
+					{
+						// Special case for clamp -- try to fold it as min(max(t, minVal), maxVal)
+						TIntermSequence &parameters = paramNode->getAsAggregate()->getSequence();
+						TIntermConstantUnion *valConstant = parameters[0]->getAsTyped()->getAsConstantUnion();
+						TIntermConstantUnion *minConstant = parameters[1]->getAsTyped()->getAsConstantUnion();
+						TIntermConstantUnion *maxConstant = parameters[2]->getAsTyped()->getAsConstantUnion();
+
+						if (valConstant && minConstant && maxConstant)
+						{
+							TIntermTyped *typedReturnNode = valConstant->fold(EOpMax, minConstant, infoSink());
+							if (typedReturnNode && typedReturnNode->getAsConstantUnion())
+							{
+								typedReturnNode = maxConstant->fold(EOpMin, typedReturnNode->getAsConstantUnion(), infoSink());
+							}
+							if (typedReturnNode)
+							{
+								callNode = typedReturnNode;
+							}
+						}
+					}
+					else
+					{
 						if(fnCandidate->getParamCount() == 2)
 						{
 							TIntermSequence &parameters = paramNode->getAsAggregate()->getSequence();
@@ -3649,6 +3672,7 @@ TIntermTyped *TParseContext::addFunctionCallOrMethod(TFunction *fnCall, TIntermN
 						}
 					}
 				}
+			}
 			else
 			{
 				// This is a real function call