Support constant folding of common built-ins

This change adds constant folding support for unary common built-ins:
abs, sign, floor, trunc, round, roundEven, ceil and fract.

BUG=angleproject:913
TEST= dEQP tests
dEQP-GLES3.functional.shaders.constant_expressions.builtin_functions.common*
(80 out of 210 tests started passing with this change)

Change-Id: I06800ed0e03764c0f7aab6bcd45c4f122de5a3c1
Reviewed-on: https://chromium-review.googlesource.com/265394
Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Olli Etuaho <oetuaho@nvidia.com>

src/compiler/translator/IntermNode.cpp

@@ -1330,6 +1330,106 @@ TIntermTyped *TIntermConstantUnion::fold(
                     tempConstArray[i].setFConst(1.0f / tempConstArray[i].getFConst());
                 break;
 
+              case EOpAbs:
+                switch (getType().getBasicType())
+                {
+                  case EbtFloat:
+                    tempConstArray[i].setFConst(std::abs(unionArray[i].getFConst()));
+                    break;
+                  case EbtInt:
+                    tempConstArray[i].setIConst(std::abs(unionArray[i].getIConst()));
+                    break;
+                  default:
+                    infoSink.info.message(
+                        EPrefixInternalError, getLine(),
+                        "Unary operation not folded into constant");
+                    return nullptr;
+                }
+                break;
+
+              case EOpSign:
+                switch (getType().getBasicType())
+                {
+                  case EbtFloat:
+                    {
+                        float fConst = unionArray[i].getFConst();
+                        float fResult = 0.0f;
+                        if (fConst > 0.0f)
+                            fResult = 1.0f;
+                        else if (fConst < 0.0f)
+                            fResult = -1.0f;
+                        tempConstArray[i].setFConst(fResult);
+                    }
+                    break;
+                  case EbtInt:
+                    {
+                        int iConst = unionArray[i].getIConst();
+                        int iResult = 0;
+                        if (iConst > 0)
+                            iResult = 1;
+                        else if (iConst < 0)
+                            iResult = -1;
+                        tempConstArray[i].setIConst(iResult);
+                    }
+                    break;
+                  default:
+                    infoSink.info.message(
+                        EPrefixInternalError, getLine(),
+                        "Unary operation not folded into constant");
+                    return nullptr;
+                }
+                break;
+
+              case EOpFloor:
+                if (!foldFloatTypeUnary(unionArray[i], static_cast<FloatTypeUnaryFunc>(&std::floor), infoSink, &tempConstArray[i]))
+                    return nullptr;
+                break;
+
+              case EOpTrunc:
+                if (!foldFloatTypeUnary(unionArray[i], static_cast<FloatTypeUnaryFunc>(&std::trunc), infoSink, &tempConstArray[i]))
+                    return nullptr;
+                break;
+
+              case EOpRound:
+                if (!foldFloatTypeUnary(unionArray[i], static_cast<FloatTypeUnaryFunc>(&std::round), infoSink, &tempConstArray[i]))
+                    return nullptr;
+                break;
+
+              case EOpRoundEven:
+                if (getType().getBasicType() == EbtFloat)
+                {
+                    float x = unionArray[i].getFConst();
+                    float result;
+                    float fractPart = std::modf(x, &result);
+                    if (std::abs(fractPart) == 0.5f)
+                        result = 2.0f * std::round(x / 2.0f);
+                    else
+                        result = std::round(x);
+                    tempConstArray[i].setFConst(result);
+                    break;
+                }
+                infoSink.info.message(
+                    EPrefixInternalError, getLine(),
+                    "Unary operation not folded into constant");
+                return nullptr;
+
+              case EOpCeil:
+                if (!foldFloatTypeUnary(unionArray[i], static_cast<FloatTypeUnaryFunc>(&std::ceil), infoSink, &tempConstArray[i]))
+                    return nullptr;
+                break;
+
+              case EOpFract:
+                if (getType().getBasicType() == EbtFloat)
+                {
+                    float x = unionArray[i].getFConst();
+                    tempConstArray[i].setFConst(x - std::floor(x));
+                    break;
+                }
+                infoSink.info.message(
+                    EPrefixInternalError, getLine(),
+                    "Unary operation not folded into constant");
+                return nullptr;
+
               default:
                 return NULL;
             }