Make all fma variants constexpr, add tests

Author: ckoparkar

clang/include/clang/Basic/Builtins.td

@@ -3885,7 +3885,7 @@ def Floor : FPMathTemplate, LibBuiltin<"math.h"> {
 
 def Fma : FPMathTemplate, LibBuiltin<"math.h"> {
   let Spellings = ["fma"];
-  let Attributes = [NoThrow, ConstIgnoringErrnoAndExceptions];
+  let Attributes = [NoThrow, ConstIgnoringErrnoAndExceptions, Constexpr];
   let Prototype = "T(T, T, T)";
   let AddBuiltinPrefixedAlias = 1;
 }

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

@@ -1742,6 +1742,19 @@ namespace Invalid {
                               // both-note {{in call to}}
 }
 
+namespace Fma {
+  static_assert(__builtin_fma(2.0, 3.0, 4.0) == 10.0);
+  static_assert(__builtin_fma(200.0, 300.0, 400.0) == 60400.0);
+  static_assert(__builtin_fmal(2.0, 3.0, 4.0) == 10.0);
+  static_assert(__builtin_fmal(200.0, 300.0, 400.0) == 60400.0);
+  static_assert(__builtin_fmaf(2.0, 3.0, 4.0) == 10.0);
+  static_assert(__builtin_fmaf(200.0, 300.0, 400.0) == 60400.0);
+  static_assert(__builtin_fmaf16(2.0, 3.0, 4.0) == 10.0);
+  static_assert(__builtin_fmaf16(200.0, 300.0, 400.0) == 60416.0);
+  static_assert(__builtin_fmaf128(2.0, 3.0, 4.0) == 10.0);
+  static_assert(__builtin_fmaf128(200.0, 300.0, 400.0) == 60400.0);
+}
+
 #if __cplusplus >= 202002L
 namespace WithinLifetime {
   constexpr int a = 10;