https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126734
Bug ID: 126734
Summary: Continuing regression in quality of generated x86
machine code for a simple bit rotation
Product: gcc
Version: 16.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: contact at ivanchev dot net
Target Milestone: ---
I have the following bit-rotation sample in a set of tools for stress-testing
compilers:
#include <stdint.h>
uint32_t func(uint32_t a) {
uint64_t b = ((uint64_t) a << 32) | a;
return (uint32_t) (b >> 16);
}
The quality of the generated machine code with "-O2 -m32" has been dropping
continuously since GCC 12.5 as is evident here:
https://godbolt.org/z/cajcb5Gz4
GCC 16.2 generates useless push / pop sequence and the trunk is straight up
suspicious whereas clang correctly identifies the pattern and emits a ROR
instruction.
