| Summary: | builtin memmove could be memcpy if src and dst don't alias | ||
|---|---|---|---|
| Product: | gcc | Reporter: | Kaveh Ghazi <ghazi> |
| Component: | middle-end | Assignee: | Richard Biener <rguenth> |
| Status: | RESOLVED FIXED | ||
| Severity: | enhancement | CC: | gcc-bugs, rguenth, sjames |
| Priority: | P2 | Keywords: | alias, missed-optimization |
| Version: | 4.1.0 | ||
| Target Milestone: | --- | ||
| See Also: | https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112653 | ||
| Host: | Target: | ||
| Build: | Known to work: | ||
| Known to fail: | Last reconfirmed: | 2010-05-09 16:54:18 | |
Confirmed. Mine. Fixed. Subject: Bug 21602 Author: rguenth Date: Mon Aug 30 13:46:31 2010 New Revision: 163646 URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=163646 Log: 2010-08-30 Richard Guenther <rguenther@suse.de> PR tree-optimization/21602 * builtins.c (fold_builtin_memory_op): Fold memmove to memcpy using points-to information. Modified: trunk/gcc/ChangeLog trunk/gcc/builtins.c |
The current builtin memmove optimizes to memcpy if it can prove that the source pointer is in readonly memory, under the assumption that the destination pointer must be writable and therefore couldn't overlap. However we could generalize this such that if we can prove the source and dest don't alias, then we can do the transformation. E.g. given the following code, we should optimize the memmove call in both foo() and bar(), however we only do foo() in mainline. typedef __SIZE_TYPE__ size_t; extern void *malloc (size_t); extern void *memmove (void *, const void *, size_t); void *foo (void) { void *dst = malloc (13); return memmove (dst, "hello world\n", 13); } void *bar (void *src) { void *dst = malloc(13); return memmove (dst, src, 13); }