Attempting to enable asserts-as-hints with isopen as an exception

The theory is that lfsr_opened_isopen is a relatively special case, and
the main cause of LFS_ASSERT side-effects. All other LFS_ASSERTs are
either limited to simple expressions, or small static-inline functions.

Unfortunately, even without lfsr_opened_isopen asserts, it seems
asserts-as-hints still results in worse code/stack costs:

                        code          stack
  no-assert (before):  33626           2552
  hint-assert (after): 33670 (+0.1%)   2592 (+1.6%)

Digging around in the low-level assembly, it seems that what is
happening is the increased number of calls to static-inline functions is
causing the compiler to prefer to not-inline functions more often. Then,
even if calls would be eliminated as dead-code, the damage is done to
the containing function.

It's not entirely clear how this could be avoided. Maybe a separate
LFS_ASSERT for only pure expressions? This may not be worth trying to
solve outside of the compiler...

This commit is contained in:

Christopher Haster

2024-06-10 00:40:49 -05:00

parent b563050fc8

commit 9c2c101e7f

2 changed files with 68 additions and 27 deletions

									
										lfs_util.h
									
		+2
		
												View File
												
				@@ -96,6 +96,8 @@ extern "C"

				#ifndef LFS_ASSERT

				#ifndef LFS_NO_ASSERT

				#define LFS_ASSERT(test) assert(test)

				#elif !defined(LFS_NO_BUILTINS)

				#define LFS_ASSERT(test) ((test) ? (void)0 : __builtin_unreachable())

				#else

				#define LFS_ASSERT(test)

				#endif