[Python-checkins] GH-90997: Improve inline cache performance for MSVC (GH-96781)

Wed Sep 14 20:06:10 EDT 2022

https://github.com/python/cpython/commit/a83fdf2563aad794f0b0a78e534313bbe050d1eb
commit: a83fdf2563aad794f0b0a78e534313bbe050d1eb
branch: main
author: Brandt Bucher <brandtbucher at microsoft.com>
committer: brandtbucher <brandtbucher at gmail.com>
date: 2022年09月14日T17:05:04-07:00
summary:
GH-90997: Improve inline cache performance for MSVC (GH-96781)
files:
A Misc/NEWS.d/next/Core and Builtins/2022-09-12-15-15-04.gh-issue-90997.sZO8c9.rst
M Include/internal/pycore_code.h

diff --git a/Include/internal/pycore_code.h b/Include/internal/pycore_code.h
index 7d5fe941fcb4..bf5945435c17 100644
--- a/Include/internal/pycore_code.h
+++ b/Include/internal/pycore_code.h
@@ -285,110 +285,55 @@ PyAPI_FUNC(PyObject*) _Py_GetSpecializationStats(void);
 #define EVAL_CALL_STAT_INC_IF_FUNCTION(name, callable) ((void)0)
 #endif // !Py_STATS
 
-// Cache values are only valid in memory, so use native endianness.
-#ifdef WORDS_BIGENDIAN
+// Utility functions for reading/writing 32/64-bit values in the inline caches.
+// Great care should be taken to ensure that these functions remain correct and
+// performant! They should compile to just "move" instructions on all supported
+// compilers and platforms.
+
+// We use memcpy to let the C compiler handle unaligned accesses and endianness
+// issues for us. It also seems to produce better code than manual copying for
+// most compilers (see https://blog.regehr.org/archives/959 for more info).
 
 static inline void
 write_u32(uint16_t *p, uint32_t val)
 {
- p[0] = (uint16_t)(val >> 16);
- p[1] = (uint16_t)(val >> 0);
+ memcpy(p, &val, sizeof(val));
 }
 
 static inline void
 write_u64(uint16_t *p, uint64_t val)
 {
- p[0] = (uint16_t)(val >> 48);
- p[1] = (uint16_t)(val >> 32);
- p[2] = (uint16_t)(val >> 16);
- p[3] = (uint16_t)(val >> 0);
-}
-
-static inline uint32_t
-read_u32(uint16_t *p)
-{
- uint32_t val = 0;
- val |= (uint32_t)p[0] << 16;
- val |= (uint32_t)p[1] << 0;
- return val;
-}
-
-static inline uint64_t
-read_u64(uint16_t *p)
-{
- uint64_t val = 0;
- val |= (uint64_t)p[0] << 48;
- val |= (uint64_t)p[1] << 32;
- val |= (uint64_t)p[2] << 16;
- val |= (uint64_t)p[3] << 0;
- return val;
-}
-
-#else
-
-static inline void
-write_u32(uint16_t *p, uint32_t val)
-{
- p[0] = (uint16_t)(val >> 0);
- p[1] = (uint16_t)(val >> 16);
+ memcpy(p, &val, sizeof(val));
 }
 
 static inline void
-write_u64(uint16_t *p, uint64_t val)
+write_obj(uint16_t *p, PyObject *val)
 {
- p[0] = (uint16_t)(val >> 0);
- p[1] = (uint16_t)(val >> 16);
- p[2] = (uint16_t)(val >> 32);
- p[3] = (uint16_t)(val >> 48);
+ memcpy(p, &val, sizeof(val));
 }
 
 static inline uint32_t
 read_u32(uint16_t *p)
 {
- uint32_t val = 0;
- val |= (uint32_t)p[0] << 0;
- val |= (uint32_t)p[1] << 16;
+ uint32_t val;
+ memcpy(&val, p, sizeof(val));
 return val;
 }
 
 static inline uint64_t
 read_u64(uint16_t *p)
 {
- uint64_t val = 0;
- val |= (uint64_t)p[0] << 0;
- val |= (uint64_t)p[1] << 16;
- val |= (uint64_t)p[2] << 32;
- val |= (uint64_t)p[3] << 48;
+ uint64_t val;
+ memcpy(&val, p, sizeof(val));
 return val;
 }
 
-#endif
-
-static inline void
-write_obj(uint16_t *p, PyObject *obj)
-{
- uintptr_t val = (uintptr_t)obj;
-#if SIZEOF_VOID_P == 8
- write_u64(p, val);
-#elif SIZEOF_VOID_P == 4
- write_u32(p, val);
-#else
- #error "SIZEOF_VOID_P must be 4 or 8"
-#endif
-}
-
 static inline PyObject *
 read_obj(uint16_t *p)
 {
- uintptr_t val;
-#if SIZEOF_VOID_P == 8
- val = read_u64(p);
-#elif SIZEOF_VOID_P == 4
- val = read_u32(p);
-#else
- #error "SIZEOF_VOID_P must be 4 or 8"
-#endif
- return (PyObject *)val;
+ PyObject *val;
+ memcpy(&val, p, sizeof(val));
+ return val;
 }
 
 /* See Objects/exception_handling_notes.txt for details.
diff --git a/Misc/NEWS.d/next/Core and Builtins/2022-09-12-15-15-04.gh-issue-90997.sZO8c9.rst b/Misc/NEWS.d/next/Core and Builtins/2022-09-12-15-15-04.gh-issue-90997.sZO8c9.rst
new file mode 100644
index 000000000000..4a43e2babcde
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2022-09-12-15-15-04.gh-issue-90997.sZO8c9.rst	
@@ -0,0 +1,2 @@
+Improve the performance of reading and writing inline bytecode caches on
+some platforms.
