glsl: Add ir_constant constructor for fp16

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3929>

src/compiler/glsl/ir.cpp

@@ -682,6 +682,19 @@ ir_constant::ir_constant(const struct glsl_type *type,
    memcpy(& this->value, data, sizeof(this->value));
 }
 
+ir_constant::ir_constant(float16_t f16, unsigned vector_elements)
+   : ir_rvalue(ir_type_constant)
+{
+   assert(vector_elements <= 4);
+   this->type = glsl_type::get_instance(GLSL_TYPE_FLOAT16, vector_elements, 1);
+   for (unsigned i = 0; i < vector_elements; i++) {
+      this->value.f16[i] = f16.bits;
+   }
+   for (unsigned i = vector_elements; i < 16; i++)  {
+      this->value.f[i] = 0;
+   }
+}
+
 ir_constant::ir_constant(float f, unsigned vector_elements)
    : ir_rvalue(ir_type_constant)
 {

src/compiler/glsl/ir.h

@@ -30,6 +30,7 @@
 
 #include "util/ralloc.h"
 #include "util/format/u_format.h"
+#include "util/half_float.h"
 #include "compiler/glsl_types.h"
 #include "list.h"
 #include "ir_visitor.h"
@@ -2190,6 +2191,7 @@ public:
    ir_constant(bool b, unsigned vector_elements=1);
    ir_constant(unsigned int u, unsigned vector_elements=1);
    ir_constant(int i, unsigned vector_elements=1);
+   ir_constant(float16_t f16, unsigned vector_elements=1);
    ir_constant(float f, unsigned vector_elements=1);
    ir_constant(double d, unsigned vector_elements=1);
    ir_constant(uint64_t u64, unsigned vector_elements=1);

src/util/half_float.h

@@ -33,8 +33,8 @@
 extern "C" {
 #endif
 
-#define FP16_ONE     0x3C00
+#define FP16_ONE     ((uint16_t) 0x3c00)
-#define FP16_ZERO    0
+#define FP16_ZERO    ((uint16_t) 0)
 
 uint16_t _mesa_float_to_half(float val);
 float _mesa_half_to_float(uint16_t val);
@@ -62,6 +62,22 @@ _mesa_half_is_negative(uint16_t h)
 }
 
 
+#ifdef __cplusplus
+
+/* Helper class for disambiguating fp16 from uint16_t in C++ overloads */
+
+struct float16_t {
+   uint16_t bits;
+   float16_t(float f) : bits(_mesa_float_to_half(f)) {}
+   float16_t(double d) : bits(_mesa_float_to_half(d)) {}
+   float16_t(uint16_t bits) : bits(bits) {}
+   static float16_t one() { return float16_t(FP16_ONE); }
+   static float16_t zero() { return float16_t(FP16_ZERO); }
+};
+
+#endif
+
+
 #ifdef __cplusplus
 } /* extern C */
 #endif