https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115437
Bug ID: 115437 Summary: Wrong optimized code - GCC didn't detect a variable is modified Product: gcc Version: 12.1.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: other Assignee: unassigned at gcc dot gnu.org Reporter: Explorer09 at gmail dot com Target Milestone: --- Note: I cannot tell which component this bug belongs to. Please help me update the "component" field for this bug report. Tested in Compiler Explorer: https://godbolt.org/z/c6fKjMboK ## Test code ```c #include <stdio.h> #include <stddef.h> #include <stdint.h> __attribute__((noinline)) \ uint32_t utf8_to_ascii(const uint8_t **sequence) { if (**sequence <= 0x7F) { return *(*sequence)++; } (*sequence)++; return (uint32_t)-1; } int main(void) { static const char str[] = { 'A', 'B', 'C', '\x00' }; static const uint8_t str2[] = { 'A', 'B', 'C', '\x00' }; uint32_t code_point; { const char *str_ptr; str_ptr = str; code_point = utf8_to_ascii((const uint8_t **)&str_ptr); printf("%p %p\n", str, str_ptr); printf("src: %lu byte(s) parsed\n", (unsigned long)(str_ptr - str)); } { const uint8_t *str_ptr2; str_ptr2 = (const uint8_t *)str; code_point = utf8_to_ascii(&str_ptr2); const char *str_ptr; str_ptr = (const char *)str_ptr2; printf("%p %p\n", str, str_ptr); printf("src: %lu byte(s) parsed\n", (unsigned long)(str_ptr - str)); } { const uint8_t *str_ptr2; str_ptr2 = str2; code_point = utf8_to_ascii(&str_ptr2); printf("%p %p\n", str2, str_ptr2); printf("src: %lu byte(s) parsed\n", (unsigned long)(str_ptr2 - str2)); } return 0; } ``` ## Expected result All three blocks in main() should print "src: 1 byte(s) parsed". ## Actual result x86_64 gcc 12.1 with "-O2" option would have the first block print "src: 0 byte(s) parsed". "-Os" would also produce the same error result. "-O0" and "-O1" are fine as far as I have tested. GCC versions 12.1 to 14.1 are those that are affected.