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* [Bug middle-end/94206] New: Wrong optimization: memset of n-bit integer types (from bit-fields) is truncated to n bits (instead of sizeof) @ 2020-03-17 21:15 ch3root at openwall dot com 2020-03-17 21:22 ` [Bug middle-end/94206] " pinskia at gcc dot gnu.org ` (5 more replies) 0 siblings, 6 replies; 7+ messages in thread From: ch3root at openwall dot com @ 2020-03-17 21:15 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94206 Bug ID: 94206 Summary: Wrong optimization: memset of n-bit integer types (from bit-fields) is truncated to n bits (instead of sizeof) Product: gcc Version: 10.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: middle-end Assignee: unassigned at gcc dot gnu.org Reporter: ch3root at openwall dot com Target Milestone: --- Bit-fields of different widths have their own types in gcc. And `memset` seems to be optimized strangely for them. Even at `-O0`! This is not standard C due to the use of `typeof` but this topic is starting to be more interesting in light of N2472 "Adding Fundamental Type for N-bit Integers". ---------------------------------------------------------------------- #include <string.h> #include <stdio.h> struct { unsigned long x:33; } s; typedef __typeof__(s.x + 0) uint33; int main() { uint33 x; printf("sizeof = %zu\n", sizeof x); memset(&x, -1, sizeof x); unsigned long u; memcpy(&u, &x, sizeof u); printf("%lx\n", u); } ---------------------------------------------------------------------- $ gcc -std=c11 -pedantic -Wall -Wextra test.c && ./a.out sizeof = 8 1ffffffff $ gcc -std=c11 -pedantic -Wall -Wextra -O3 test.c && ./a.out sizeof = 8 1ffffffff ---------------------------------------------------------------------- gcc x86-64 version: gcc (GCC) 10.0.1 20200317 (experimental) ---------------------------------------------------------------------- The right result is `ffffffffffffffff`. ^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug middle-end/94206] Wrong optimization: memset of n-bit integer types (from bit-fields) is truncated to n bits (instead of sizeof) 2020-03-17 21:15 [Bug middle-end/94206] New: Wrong optimization: memset of n-bit integer types (from bit-fields) is truncated to n bits (instead of sizeof) ch3root at openwall dot com @ 2020-03-17 21:22 ` pinskia at gcc dot gnu.org 2020-03-18 8:12 ` rguenth at gcc dot gnu.org ` (4 subsequent siblings) 5 siblings, 0 replies; 7+ messages in thread From: pinskia at gcc dot gnu.org @ 2020-03-17 21:22 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94206 --- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- This again padding bits. ^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug middle-end/94206] Wrong optimization: memset of n-bit integer types (from bit-fields) is truncated to n bits (instead of sizeof) 2020-03-17 21:15 [Bug middle-end/94206] New: Wrong optimization: memset of n-bit integer types (from bit-fields) is truncated to n bits (instead of sizeof) ch3root at openwall dot com 2020-03-17 21:22 ` [Bug middle-end/94206] " pinskia at gcc dot gnu.org @ 2020-03-18 8:12 ` rguenth at gcc dot gnu.org 2020-03-18 12:12 ` cvs-commit at gcc dot gnu.org ` (3 subsequent siblings) 5 siblings, 0 replies; 7+ messages in thread From: rguenth at gcc dot gnu.org @ 2020-03-18 8:12 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94206 Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Ever confirmed|0 |1 Last reconfirmed| |2020-03-18 Assignee|unassigned at gcc dot gnu.org |rguenth at gcc dot gnu.org Status|UNCONFIRMED |ASSIGNED Known to fail| |4.8.5 --- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> --- Broken since long via memset folding: __MEM <uint33> ((void *)&x) = _Literal (uint33) 8589934591; ^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug middle-end/94206] Wrong optimization: memset of n-bit integer types (from bit-fields) is truncated to n bits (instead of sizeof) 2020-03-17 21:15 [Bug middle-end/94206] New: Wrong optimization: memset of n-bit integer types (from bit-fields) is truncated to n bits (instead of sizeof) ch3root at openwall dot com 2020-03-17 21:22 ` [Bug middle-end/94206] " pinskia at gcc dot gnu.org 2020-03-18 8:12 ` rguenth at gcc dot gnu.org @ 2020-03-18 12:12 ` cvs-commit at gcc dot gnu.org 2020-03-18 12:13 ` rguenth at gcc dot gnu.org ` (2 subsequent siblings) 5 siblings, 0 replies; 7+ messages in thread From: cvs-commit at gcc dot gnu.org @ 2020-03-18 12:12 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94206 --- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Richard Biener <rguenth@gcc.gnu.org>: https://gcc.gnu.org/g:1ba9acb11e3589b96ed945ed2a3af6acd6377018 commit r10-7242-g1ba9acb11e3589b96ed945ed2a3af6acd6377018 Author: Richard Biener <rguenther@suse.de> Date: Wed Mar 18 13:11:30 2020 +0100 middle-end/94206 fix memset folding to avoid types with padding This makes sure that the store a memset is folded to uses a type covering all bits. 2020-03-18 Richard Biener <rguenther@suse.de> PR middle-end/94206 * gimple-fold.c (gimple_fold_builtin_memset): Avoid using partial int modes or not mode-precision integer types for the store. * gcc.dg/torture/pr94206.c: New testcase. ^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug middle-end/94206] Wrong optimization: memset of n-bit integer types (from bit-fields) is truncated to n bits (instead of sizeof) 2020-03-17 21:15 [Bug middle-end/94206] New: Wrong optimization: memset of n-bit integer types (from bit-fields) is truncated to n bits (instead of sizeof) ch3root at openwall dot com ` (2 preceding siblings ...) 2020-03-18 12:12 ` cvs-commit at gcc dot gnu.org @ 2020-03-18 12:13 ` rguenth at gcc dot gnu.org 2020-04-02 14:49 ` cvs-commit at gcc dot gnu.org 2020-04-15 9:59 ` rguenth at gcc dot gnu.org 5 siblings, 0 replies; 7+ messages in thread From: rguenth at gcc dot gnu.org @ 2020-03-18 12:13 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94206 Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Keywords| |wrong-code Known to work| |10.0 --- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> --- Fixed on trunk sofar. ^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug middle-end/94206] Wrong optimization: memset of n-bit integer types (from bit-fields) is truncated to n bits (instead of sizeof) 2020-03-17 21:15 [Bug middle-end/94206] New: Wrong optimization: memset of n-bit integer types (from bit-fields) is truncated to n bits (instead of sizeof) ch3root at openwall dot com ` (3 preceding siblings ...) 2020-03-18 12:13 ` rguenth at gcc dot gnu.org @ 2020-04-02 14:49 ` cvs-commit at gcc dot gnu.org 2020-04-15 9:59 ` rguenth at gcc dot gnu.org 5 siblings, 0 replies; 7+ messages in thread From: cvs-commit at gcc dot gnu.org @ 2020-04-02 14:49 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94206 --- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-9 branch has been updated by Richard Biener <rguenth@gcc.gnu.org>: https://gcc.gnu.org/g:4b1087f8dc7505997dc475b554b5b86a06c78d69 commit r9-8443-g4b1087f8dc7505997dc475b554b5b86a06c78d69 Author: Richard Biener <rguenther@suse.de> Date: Wed Mar 18 13:11:30 2020 +0100 middle-end/94206 fix memset folding to avoid types with padding This makes sure that the store a memset is folded to uses a type covering all bits. 2020-03-18 Richard Biener <rguenther@suse.de> PR middle-end/94206 * gimple-fold.c (gimple_fold_builtin_memset): Avoid using partial int modes or not mode-precision integer types for the store. * gcc.dg/torture/pr94206.c: New testcase. ^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug middle-end/94206] Wrong optimization: memset of n-bit integer types (from bit-fields) is truncated to n bits (instead of sizeof) 2020-03-17 21:15 [Bug middle-end/94206] New: Wrong optimization: memset of n-bit integer types (from bit-fields) is truncated to n bits (instead of sizeof) ch3root at openwall dot com ` (4 preceding siblings ...) 2020-04-02 14:49 ` cvs-commit at gcc dot gnu.org @ 2020-04-15 9:59 ` rguenth at gcc dot gnu.org 5 siblings, 0 replies; 7+ messages in thread From: rguenth at gcc dot gnu.org @ 2020-04-15 9:59 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94206 Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Resolution|--- |FIXED Status|ASSIGNED |RESOLVED --- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> --- Fixed. ^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2020-04-15 9:59 UTC | newest] Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2020-03-17 21:15 [Bug middle-end/94206] New: Wrong optimization: memset of n-bit integer types (from bit-fields) is truncated to n bits (instead of sizeof) ch3root at openwall dot com 2020-03-17 21:22 ` [Bug middle-end/94206] " pinskia at gcc dot gnu.org 2020-03-18 8:12 ` rguenth at gcc dot gnu.org 2020-03-18 12:12 ` cvs-commit at gcc dot gnu.org 2020-03-18 12:13 ` rguenth at gcc dot gnu.org 2020-04-02 14:49 ` cvs-commit at gcc dot gnu.org 2020-04-15 9:59 ` rguenth at gcc dot gnu.org
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