https://llvm.org/bugs/show_bug.cgi?id=31410
Bug ID: 31410
Summary: No strict aliasing for uint8_t
Product: clang
Version: unspecified
Hardware: All
OS: All
Status: NEW
Severity: normal
Priority: P
Component: -New Bugs
Assignee: unassignedclangb...@nondot.org
Reporter: rsilv...@google.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
Currently uint8_t is treated identically to an unsigned char for purposes
of strict aliasing. This is unnecessary and results in missed optimization,
since unsigned chars must alias all other types (but uint8_ts are not required
to).
There is a related discussion at
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66110
Here is a trivial demonstration:
#include <stdint.h>
int strict(uint32_t *p, uint8_t *q) {
*p = 1;
*q = 0;
return *p;
}
With clang -O on x86-64, we get:
mov dword ptr [rdi], 1
mov byte ptr [rsi], 0
mov eax, dword ptr [rdi]
ret
Replacing uint8_t with uint16_t (note the load immediate into eax):
mov dword ptr [rdi], 1
mov word ptr [rsi], 0
mov eax, 1
ret
--
You are receiving this mail because:
You are on the CC list for the bug.
_______________________________________________
llvm-bugs mailing list
llvm-bugs@lists.llvm.org
http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
