https://gcc.gnu.org/bugzilla/show_bug.cgi?id=15533
--- Comment #6 from Uroš Bizjak <ubizjak at gmail dot com> --- (In reply to Cesar Eduardo Barros from comment #0) > When compiling: > #include <stdint.h> > #define regparm __attribute__((regparm(3))) > uint8_t a; > uint16_t regparm fn(uint16_t b) > { return (b & ~0xFF) | a; } This should probably be optimized in match.pd to BIT_INSERT_EXPR.