[ROCm] Reduce duplication in bfloat16_support_literal definition (pytorch#166147)

This PR refactors the bfloat16_support_literal constant in the PyTorch build logic to eliminate duplicated ROCm-specific code.

Previously, there were two nearly identical branches for ROCM_VERSION < 70000 and ROCM_VERSION >= 70000, differing only by a single typedef. These have been unified into one conditional block with a minimal version guard inside. (#2502)

Pull Request resolved: pytorch#166147
Approved by: https://github.com/jerrymannil, https://github.com/jeffdaily

Author: rraminen

torch/csrc/jit/codegen/fuser/cuda/resource_strings.h

@@ -260,82 +260,20 @@ typedef __half half;
 )";
 #endif
 
-#if defined(USE_ROCM) && ROCM_VERSION < 70000
-constexpr auto bfloat16_support_literal =
-    R"(
-#ifndef __align__
-#define __align__(x) __attribute__((aligned(x)))
-#endif
-
-typedef struct __align__(2) {
-  unsigned short x;
-}
-__nv_bfloat16_raw;
-
-#if defined(__cplusplus)
-struct __align__(2) __nv_bfloat16 {
-  __host__ __device__ __nv_bfloat16() {}
-
-  __host__ __device__ __nv_bfloat16& operator=(const __nv_bfloat16_raw& hr) {
-    __x = hr.x;
-    return *this;
-  }
-
-  unsigned short __x;
-};
-
-__device__ unsigned short __internal_float2bfloat16(
-    const float f,
-    unsigned int& sign,
-    unsigned int& remainder) {
-  unsigned int x;
-
-  x = __float_as_uint(f);
-
-  if ((x & 0x7fffffffU) > 0x7f800000U) {
-    sign = 0U;
-    remainder = 0U;
-    return static_cast<unsigned short>(0x7fffU);
-  }
-  sign = x >> 31;
-  remainder = x << 16;
-  return static_cast<unsigned short>(x >> 16);
-}
+#if defined(USE_ROCM)
 
-/* Definitions of intrinsics */
-__device__ __nv_bfloat16 __float2bfloat16(const float a) {
-  __nv_bfloat16 val;
-  __nv_bfloat16_raw r;
-  unsigned int sign;
-  unsigned int remainder;
-  r.x = __internal_float2bfloat16(a, sign, remainder);
-  if ((remainder > 0x80000000U) ||
-      ((remainder == 0x80000000U) && ((r.x & 0x1U) != 0U))) {
-    r.x++;
-  }
-  val = r;
-  return val;
-}
+#if ROCM_VERSION >= 70000
+#define BF16_UINT32_DEF "typedef unsigned int uint32_t;\n"
+#else
+#define BF16_UINT32_DEF ""
+#endif
 
-__device__ float __bfloat162float(const __nv_bfloat16 a) {
-  union
-  {
-      uint32_t int32;
-      float    fp32;
-  } u = {uint32_t(a.__x) << 16};
-  return u.fp32;
-}
-#endif /* defined(__cplusplus) */
-)";
-#elif defined(USE_ROCM) && ROCM_VERSION >= 70000
 constexpr auto bfloat16_support_literal =
     R"(
 #ifndef __align__
 #define __align__(x) __attribute__((aligned(x)))
 #endif
-
-typedef unsigned int uint32_t;
-
+)" BF16_UINT32_DEF R"(
 typedef struct __align__(2) {
   unsigned short x;
 }