[clang][Interp] Implement __builtin_fmin

Differential Revision: https://reviews.llvm.org/D155546

Author: tbaederr

clang/lib/AST/Interp/InterpBuiltin.cpp

@@ -143,6 +143,25 @@ static bool interp__builtin_copysign(InterpState &S, CodePtr OpPC,
   return true;
 }
 
+static bool interp__builtin_fmin(InterpState &S, CodePtr OpPC,
+                                 const InterpFrame *Frame, const Function *F) {
+  const Floating &LHS = getParam<Floating>(Frame, 0);
+  const Floating &RHS = getParam<Floating>(Frame, 1);
+
+  Floating Result;
+
+  // When comparing zeroes, return -0.0 if one of the zeroes is negative.
+  if (LHS.isZero() && RHS.isZero() && RHS.isNegative())
+    Result = RHS;
+  else if (LHS.isNan() || RHS < LHS)
+    Result = RHS;
+  else
+    Result = LHS;
+
+  S.Stk.push<Floating>(Result);
+  return true;
+}
+
 bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const Function *F) {
   InterpFrame *Frame = S.Current;
   APValue Dummy;
@@ -195,6 +214,15 @@ bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const Function *F) {
       return Ret<PT_Float>(S, OpPC, Dummy);
     break;
 
+  case Builtin::BI__builtin_fmin:
+  case Builtin::BI__builtin_fminf:
+  case Builtin::BI__builtin_fminl:
+  case Builtin::BI__builtin_fminf16:
+  case Builtin::BI__builtin_fminf128:
+    if (interp__builtin_fmin(S, OpPC, Frame, F))
+      return Ret<PT_Float>(S, OpPC, Dummy);
+    break;
+
   default:
     return false;
   }

clang/test/AST/Interp/builtin-functions.cpp

@@ -60,3 +60,15 @@ namespace nan {
                                              // expected-note {{read of dereferenced one-past-the-end pointer}} \
                                              // expected-note {{in call to}}
 }
+
+namespace fmin {
+  constexpr float f1 = __builtin_fmin(1.0, 2.0f);
+  static_assert(f1 == 1.0f, "");
+
+  constexpr float min = __builtin_fmin(__builtin_nan(""), 1);
+  static_assert(min == 1, "");
+  constexpr float min2 = __builtin_fmin(1, __builtin_nan(""));
+  static_assert(min2 == 1, "");
+  constexpr float min3 = __builtin_fmin(__builtin_inf(), __builtin_nan(""));
+  static_assert(min3 == __builtin_inf(), "");
+}