http://llvm.org/bugs/show_bug.cgi?id=3756
Summary: __attribute__((always_inline)) and __builtin_constant_p
Product: tools
Version: 2.5
Platform: PC
OS/Version: Linux
Status: NEW
Severity: normal
Priority: P2
Component: llvm-gcc
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
Created an attachment (id=2683)
--> (http://llvm.org/bugs/attachment.cgi?id=2683)
the sample source
llvm-gcc doesn't fold __builtin_constant_p inside
__attribute__((always_inline)) functions. The example is simple, in our code we
have:
__attribute__((always_inline)) static inline
void ifree(void *mem, mem_flags_t flags)
{
if (__builtin_constant_p(mem)) {
if (mem == NULL)
return;
}
if (__builtin_constant_p(flags)) {
switch (flags & MEM_POOL_MASK) {
case MEM_LIBC:
free(mem);
return;
default:
break;
}
}
__ifree(mem, flags);
}
We have lots of calls that look like: ifree(some_pointer, MEM_LIBC), and gcc
properly does constant folding. but llvm-gcc does not.
Attached are a C file, the .S file generated by gcc and the .S file generated
by llvm, where you can see that the former sees it should use a straight free()
call, and the latter calls __ifree.
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