[AST] Add fixed-point division constant evaluation.

Reviewers: rjmccall, leonardchan, bjope

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D73187

Author: bevin-hansson

clang/include/clang/Basic/FixedPoint.h

@@ -130,6 +130,7 @@ class APFixedPoint {
    APFixedPoint add(const APFixedPoint &Other, bool *Overflow = nullptr) const;
    APFixedPoint sub(const APFixedPoint &Other, bool *Overflow = nullptr) const;
    APFixedPoint mul(const APFixedPoint &Other, bool *Overflow = nullptr) const;
+   APFixedPoint div(const APFixedPoint &Other, bool *Overflow = nullptr) const;
 
    /// Perform a unary negation (-X) on this fixed point type, taking into
    /// account saturation if applicable.

clang/lib/AST/ExprConstant.cpp

@@ -12948,6 +12948,15 @@ bool FixedPointExprEvaluator::VisitBinaryOperator(const BinaryOperator *E) {
       return false;
     return Success(Result, E);
   }
+  case BO_Div: {
+    bool AddOverflow, ConversionOverflow;
+    APFixedPoint Result = LHSFX.div(RHSFX, &AddOverflow)
+                               .convert(ResultFXSema, &ConversionOverflow);
+    if ((AddOverflow || ConversionOverflow) &&
+        !HandleOverflow(Info, E, Result, E->getType()))
+      return false;
+    return Success(Result, E);
+  }
   default:
     return false;
   }

clang/lib/Basic/FixedPoint.cpp

@@ -254,6 +254,61 @@ APFixedPoint APFixedPoint::mul(const APFixedPoint &Other,
                       CommonFXSema);
 }
 
+APFixedPoint APFixedPoint::div(const APFixedPoint &Other,
+                               bool *Overflow) const {
+  auto CommonFXSema = Sema.getCommonSemantics(Other.getSemantics());
+  APFixedPoint ConvertedThis = convert(CommonFXSema);
+  APFixedPoint ConvertedOther = Other.convert(CommonFXSema);
+  llvm::APSInt ThisVal = ConvertedThis.getValue();
+  llvm::APSInt OtherVal = ConvertedOther.getValue();
+  bool Overflowed = false;
+
+  // Widen the LHS and RHS so we can perform a full division.
+  unsigned Wide = CommonFXSema.getWidth() * 2;
+  if (CommonFXSema.isSigned()) {
+    ThisVal = ThisVal.sextOrSelf(Wide);
+    OtherVal = OtherVal.sextOrSelf(Wide);
+  } else {
+    ThisVal = ThisVal.zextOrSelf(Wide);
+    OtherVal = OtherVal.zextOrSelf(Wide);
+  }
+
+  // Upscale to compensate for the loss of precision from division, and
+  // perform the full division.
+  ThisVal = ThisVal.shl(CommonFXSema.getScale());
+  llvm::APSInt Result;
+  if (CommonFXSema.isSigned()) {
+    llvm::APInt Rem;
+    llvm::APInt::sdivrem(ThisVal, OtherVal, Result, Rem);
+    // If the quotient is negative and the remainder is nonzero, round
+    // towards negative infinity by subtracting epsilon from the result.
+    if (Result.isNegative() && !Rem.isNullValue())
+      Result = Result - 1;
+  } else
+    Result = ThisVal.udiv(OtherVal);
+  Result.setIsSigned(CommonFXSema.isSigned());
+
+  // If our result lies outside of the representative range of the common
+  // semantic, we either have overflow or saturation.
+  llvm::APSInt Max = APFixedPoint::getMax(CommonFXSema).getValue()
+                                                       .extOrTrunc(Wide);
+  llvm::APSInt Min = APFixedPoint::getMin(CommonFXSema).getValue()
+                                                       .extOrTrunc(Wide);
+  if (CommonFXSema.isSaturated()) {
+    if (Result < Min)
+      Result = Min;
+    else if (Result > Max)
+      Result = Max;
+  } else
+    Overflowed = Result < Min || Result > Max;
+
+  if (Overflow)
+    *Overflow = Overflowed;
+
+  return APFixedPoint(Result.sextOrTrunc(CommonFXSema.getWidth()),
+                      CommonFXSema);
+}
+
 void APFixedPoint::toString(llvm::SmallVectorImpl<char> &Str) const {
   llvm::APSInt Val = getValue();
   unsigned Scale = getScale();

clang/test/Frontend/fixed_point_div.c

@@ -1,6 +1,70 @@
 // RUN: %clang_cc1 -ffixed-point -triple x86_64-unknown-linux-gnu -S -emit-llvm %s -o - | FileCheck %s --check-prefixes=CHECK,SIGNED
 // RUN: %clang_cc1 -ffixed-point -triple x86_64-unknown-linux-gnu -fpadding-on-unsigned-fixed-point -S -emit-llvm %s -o - | FileCheck %s --check-prefixes=CHECK,UNSIGNED
 
+// Division between different fixed point types
+short _Accum sa_const = 1.0hk / 2.0hk;  // CHECK-DAG: @sa_const  = {{.*}}global i16 64, align 2
+_Accum a_const = 1.0hk / 2.0k;          // CHECK-DAG: @a_const   = {{.*}}global i32 16384, align 4
+long _Accum la_const = 1.0hk / 2.0lk;   // CHECK-DAG: @la_const  = {{.*}}global i64 1073741824, align 8
+short _Accum sa_const2 = 0.5hr / 2.0hk; // CHECK-DAG: @sa_const2  = {{.*}}global i16 32, align 2
+short _Accum sa_const3 = 0.5r / 2.0hk;  // CHECK-DAG: @sa_const3  = {{.*}}global i16 32, align 2
+short _Accum sa_const4 = 0.5lr / 2.0hk; // CHECK-DAG: @sa_const4  = {{.*}}global i16 32, align 2
+short _Accum sa_const5 = 2.0hk / 0.5lr; // CHECK-DAG: @sa_const5  = {{.*}}global i16 512, align 2
+
+// Unsigned division
+unsigned short _Accum usa_const = 3.0uhk / 2.0uhk;
+// CHECK-SIGNED-DAG:   @usa_const = {{.*}}global i16 192, align 2
+// CHECK-UNSIGNED-DAG: @usa_const = {{.*}}global i16 384, align 2
+
+// Unsigned / signed
+short _Accum sa_const6 = 1.0uhk / 2.0hk;
+// CHECK-DAG: @sa_const6 = {{.*}}global i16 64, align 2
+
+// Division with negative number
+short _Accum sa_const7 = 0.5hr / (-2.0hk);
+// CHECK-DAG: @sa_const7 = {{.*}}global i16 -32, align 2
+
+// Int division
+unsigned short _Accum usa_const2 = 2 / 0.5uhk;
+// CHECK-SIGNED-DAG:   @usa_const2 = {{.*}}global i16 512, align 2
+// CHECK-UNSIGNED-DAG: @usa_const2 = {{.*}}global i16 1024, align 2
+short _Accum sa_const8 = 2 / (-0.5hk);   // CHECK-DAG: @sa_const8 = {{.*}}global i16 -512, align 2
+short _Accum sa_const9 = 256 / 2.0hk;    // CHECK-DAG: @sa_const9 = {{.*}}global i16 16384, align 2
+long _Fract lf_const = 0.5lr / -1;       // CHECK-DAG: @lf_const  = {{.*}}global i32 -1073741824, align 4
+
+// Saturated division
+_Sat short _Accum sat_sa_const = (_Sat short _Accum)128.0hk / (-0.25hk);
+// CHECK-DAG: @sat_sa_const = {{.*}}global i16 -32768, align 2
+_Sat unsigned short _Accum sat_usa_const = (_Sat unsigned short _Accum)128.0uhk / (0.25uhk);
+// CHECK-SIGNED-DAG:   @sat_usa_const = {{.*}}global i16 65535, align 2
+// CHECK-UNSIGNED-DAG: @sat_usa_const = {{.*}}global i16 32767, align 2
+_Sat short _Accum sat_sa_const2 = (_Sat short _Accum)-128.0hk / (-0.0125hr);
+// CHECK-DAG: @sat_sa_const2 = {{.*}}global i16 32767, align 2
+_Sat unsigned short _Accum sat_usa_const2 = (_Sat unsigned short _Accum)128.0uhk / (-128);
+// CHECK-SIGNED-DAG:   @sat_usa_const2 = {{.*}}global i16 65535, align 2
+// CHECK-UNSIGNED-DAG: @sat_usa_const2 = {{.*}}global i16 32767, align 2
+_Sat unsigned short _Accum sat_usa_const3 = (_Sat unsigned short _Accum)0.5uhk / -1;
+// CHECK-DAG:   @sat_usa_const3 = {{.*}}global i16 0, align 2
+_Sat short _Accum sat_sa_const3 = (_Sat short _Accum)-128.0hk / 128;
+// CHECK-DAG: @sat_sa_const3 = {{.*}}global i16 -128, align 2
+_Sat short _Accum sat_sa_const4 = (_Sat short _Accum)-25.7hk / 0.1lk;
+// CHECK-DAG: @sat_sa_const4 = {{.*}}global i16 -32768, align 2
+
+// Some more cases
+short _Accum sa_const10 = 255.9921875hk / 255.9921875hk;
+// CHECK-DAG: @sa_const10 = {{.*}}global i16 128, align 2
+short _Accum sat_sa_const5 = (_Sat short _Accum)(-255.0hk - 1.0hk) / 0.0078125hk;
+// CHECK-DAG: @sat_sa_const5 = {{.*}}global i16 -32768, align 2
+_Sat short _Accum sat_sa_const6 = (_Sat short _Accum)(-255.0hk - 1.0hk) / -0.0078125hk;
+// CHECK-DAG: @sat_sa_const6 = {{.*}}global i16 32767, align 2
+short _Accum sa_const12 = 255.9921875hk / -1.0hk;
+// CHECK-DAG: @sa_const12 = {{.*}}global i16 -32767, align 2
+_Sat short _Accum sat_sa_const7 = (_Sat short _Accum)(-255.0hk - 1.0hk) / -1.0hk;
+// CHECK-DAG: @sat_sa_const7 = {{.*}}global i16 32767, align 2
+short _Accum sa_const13 = 0.0234375hk / 2.0hk;
+// CHECK-DAG: @sa_const13 = {{.*}}global i16 1, align 2
+short _Accum sa_const14 = -0.0234375hk / 2.0hk;
+// CHECK-DAG: @sa_const14 = {{.*}}global i16 -2, align 2
+
 void SignedDivision() {
   // CHECK-LABEL: SignedDivision
   short _Accum sa;