http://llvm.org/bugs/show_bug.cgi?id=18415
Bug ID: 18415
Summary: Instrinsics don't honour -mregparm=3 on i386
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: Target Description Classes
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
Consider the following test case.
void *foo(void *dest, const void *src, int n);
void *memcpy(void *dest, const void *src, int n);
void use_foo(void *dest, const void *src, int n)
{
foo(dest, src, n);
}
void use_builtin(void *dest, const void *src, int n)
{
__builtin_memcpy(dest, src, n);
}
int use_memcpy(void *dest, const void *src, int n)
{
memcpy(dest, src, n);
}
Compile with:
clang -S -o- -m32 foo.c -Os -mregparm=3
We expect each function to look something like this:
use_foo: # @use_foo
# BB#0: # %entry
jmp foo # TAILCALL
But the call to __builtin_memcpy() will put its arguments on the *stack*,
ignoring the fact that it was told mregparm=3:
use_builtin: # @use_builtin
# BB#0: # %entry
subl $12, %esp
movl %ecx, 8(%esp)
movl %edx, 4(%esp)
movl %eax, (%esp)
calll memcpy
addl $12, %esp
retl
Depending on whether we add -ffreestanding/-fno-builtin, the call to plain
"memcpy" may do one or the other.
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