https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108938
Bug ID: 108938 Summary: Missing bswap detection Product: gcc Version: 13.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: target Assignee: unassigned at gcc dot gnu.org Reporter: crazylht at gmail dot com Target Milestone: --- This is the x86 version of this bug. +++ This bug was initially created as a clone of Bug #108874 +++ If we look at the arm testcases in gcc.target/arm/rev16.c typedef unsigned int __u32; __u32 __rev16_32_alt (__u32 x) { return (((__u32)(x) & (__u32)0xff00ff00UL) >> 8) | (((__u32)(x) & (__u32)0x00ff00ffUL) << 8); } __u32 __rev16_32 (__u32 x) { return (((__u32)(x) & (__u32)0x00ff00ffUL) << 8) | (((__u32)(x) & (__u32)0xff00ff00UL) >> 8); } we should be able to generate bswap instructions for x86 GCC fails to do so and generates: __rev16_32_alt(unsigned int): mov eax, edi sal edi, 8 shr eax, 8 and edi, -16711936 and eax, 16711935 or eax, edi ret __rev16_32(unsigned int): mov eax, edi shr edi, 8 sal eax, 8 and edi, 16711935 and eax, -16711936 or eax, edi ret whereas clang manages to recognise it all into: __rev16_32_alt(unsigned int): # @__rev16_32_alt(unsigned int) mov eax, edi bswap eax ror eax, 16 ret __rev16_32(unsigned int): # @__rev16_32(unsigned int) mov eax, edi bswap eax ror eax, 16 ret