[clang][bytecode] Implement fixed-point-to-float casts (#110369)

Author: tbaederr

clang/lib/AST/ByteCode/Compiler.cpp

@@ -691,6 +691,12 @@ bool Compiler<Emitter>::VisitCastExpr(const CastExpr *CE) {
     std::memcpy(&I, &Sem, sizeof(Sem));
     return this->emitCastFloatingFixedPoint(I, CE);
   }
+  case CK_FixedPointToFloating: {
+    if (!this->visit(SubExpr))
+      return false;
+    const auto *TargetSemantics = &Ctx.getFloatSemantics(CE->getType());
+    return this->emitCastFixedPointFloating(TargetSemantics, CE);
+  }
 
   case CK_ToVoid:
     return discard(SubExpr);

clang/lib/AST/ByteCode/FixedPoint.h

@@ -52,6 +52,10 @@ class FixedPoint final {
   unsigned bitWidth() const { return V.getWidth(); }
   bool isSigned() const { return V.isSigned(); }
 
+  llvm::APFloat toFloat(const llvm::fltSemantics *Sem) const {
+    return V.convertToFloat(*Sem);
+  }
+
   ComparisonCategoryResult compare(const FixedPoint &Other) const {
     if (Other.V == V)
       return ComparisonCategoryResult::Equal;

clang/lib/AST/ByteCode/Interp.h

@@ -2367,6 +2367,14 @@ static inline bool CastFloatingFixedPoint(InterpState &S, CodePtr OpPC,
   return true;
 }
 
+static inline bool CastFixedPointFloating(InterpState &S, CodePtr OpPC,
+                                          const llvm::fltSemantics *Sem) {
+  const auto &Fixed = S.Stk.pop<FixedPoint>();
+
+  S.Stk.push<Floating>(Fixed.toFloat(Sem));
+  return true;
+}
+
 static inline bool PtrPtrCast(InterpState &S, CodePtr OpPC, bool SrcIsVoidPtr) {
   const auto &Ptr = S.Stk.peek<Pointer>();
 

clang/lib/AST/ByteCode/Opcodes.td

@@ -682,6 +682,9 @@ def CastIntegralFixedPoint : Opcode {
 def CastFloatingFixedPoint : Opcode {
   let Args = [ArgUint32];
 }
+def CastFixedPointFloating : Opcode {
+  let Args = [ArgFltSemantics];
+}
 
 def PtrPtrCast : Opcode {
   let Args = [ArgBool];

clang/test/AST/ByteCode/fixed-point.cpp

@@ -31,4 +31,7 @@ namespace FloatToFixedPointCast {
                              // both-note {{outside the range of representable values of type 'const _Fract'}}
 
   constexpr _Fract sf2 = 0.5;
+  static_assert(sf2 == 0.5);
+  constexpr float sf2f = sf2;
+  static_assert(sf2f == 0.5);
 }