https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99082
Bug ID: 99082
Summary: manual bit-field creation followed by manual
extraction does not always produce good code
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: pinskia at gcc dot gnu.org
Target Milestone: ---
Take:
#include <stdint.h>
static inline uint16_t foo(uint32_t *r8b8g8x)
{
const uint8_t r8 = *r8b8g8x;
const uint8_t b8 = *r8b8g8x >> 8;
const uint8_t g8 = *r8b8g8x >> 16;
return
(uint16_t)r8 >> 3 |
((uint16_t)(g8 >> 2) << 5) |
((uint16_t)(b8 >> 3) << 11);
}
uint16_t bar(
uint8_t *r8,
uint8_t *g8,
uint8_t *b8)
{
uint32_t t = (uint32_t)*r8 |
((uint32_t)*b8 << 8) |
((uint32_t)*g8 << 16);
return foo(&t);
}
uint16_t bar1(
uint8_t *r8,
uint8_t *g8,
uint8_t *b8)
{
return
(uint16_t)*r8 >> 3 |
((uint16_t)(*g8 >> 2) << 5) |
((uint16_t)(*b8 >> 3) << 11);
}
---- CUT ----
bar and bar1 should produce the same code but currently does not.
