[ADT] Fix Incorrect rounding for APFixedPoint::getIntPart

[uabelho]

I've confirmed that this fixes the problem I reported in
https://reviews.llvm.org/D134725#3842861

[uabelho]

Thanks!

[Tyker]

pushed as 2c7b7eca85c2ccc9b0d5c65169213ce499652f92

llvm/include/llvm/ADT/APFixedPoint.h

public:
   /// Return the integral part of this fixed point number, rounded towards
   /// zero. (-2.5k -> -2)
   APSInt getIntPart() const {
     if (getMsbWeight() < 0)
       return APSInt(APInt::getZero(getWidth()), Val.isUnsigned());
     APSInt ExtVal =
         (getLsbWeight() > 0) ? Val.extend(getWidth() + getLsbWeight()) : Val;
     if (Val < 0 && Val != -Val) // Cover the case when we have the min val
-      return -(-ExtVal.relativeShl(getLsbWeight()));
+      return -((-ExtVal).relativeShl(getLsbWeight()));
     return ExtVal.relativeShl(getLsbWeight());
   }
 
   /// Return the integral part of this fixed point number, rounded towards
   /// zero. The value is stored into an APSInt with the provided width and sign.
   /// If the overflow parameter is provided, and the integral value is not able
   /// to be fully stored in the provided width and sign, the overflow parameter
   /// is set to true.

llvm/unittests/ADT/APFixedPointTest.cpp

EXPECT_TRUE(APSInt::compareValues(APFixedPoint::getMin(Sema).getIntPart(),
                                     APSInt::get(Expected)) == 0);
 }
 
 void CheckIntPartMax(const FixedPointSemantics &Sema, uint64_t Expected) {
   EXPECT_TRUE(APSInt::compareValues(APFixedPoint::getMax(Sema).getIntPart(),
                                     APSInt::getUnsigned(Expected)) == 0);
 }
 
+void CheckIntPartRes(const FixedPointSemantics &Sema, int64_t Representation, int64_t Result) {
+  APFixedPoint Val(Representation, Sema);
+  ASSERT_EQ(Val.getIntPart().getZExtValue(), Result) ;
+}
+
 TEST(FixedPoint, getIntPart) {
   // Normal values
   CheckIntPart(getSAccumSema(), 2);
   CheckIntPart(getAccumSema(), 2);
   CheckIntPart(getLAccumSema(), 2);
   CheckIntPart(getUSAccumSema(), 2);
   CheckIntPart(getUAccumSema(), 2);
   CheckIntPart(getULAccumSema(), 2);
TEST(FixedPoint, getIntPart) {
   // Max
   CheckIntPartMax(getPadUSAccumSema(), 255);
   CheckIntPartMax(getPadUAccumSema(), 65535);
   CheckIntPartMax(getPadULAccumSema(), 4294967295);
 
   CheckIntPartMax(getPadUSFractSema(), 0);
   CheckIntPartMax(getPadUFractSema(), 0);
   CheckIntPartMax(getPadULFractSema(), 0);
+
+  // Rounded Towards Zero
+  CheckIntPartRes(getSFractSema(), -127, 0);
+  CheckIntPartRes(getFractSema(), -32767, 0);
+  CheckIntPartRes(getLFractSema(), -2147483647, 0);
+  CheckIntPartRes(getS16Neg18(), -32768, 0);
 }
 
 TEST(FixedPoint, compare) {
   // Equality
   // With fractional part (2.5)
   // Across sizes
   ASSERT_EQ(APFixedPoint(320, getSAccumSema()),
             APFixedPoint(81920, getAccumSema()));