PATCH: Properly generate X32 IE sequence

[H.J. Lu]

On Sun, Mar 18, 2012 at 1:55 PM, Uros Bizjak <ubizjak@gmail.com> wrote:
> On Sun, Mar 18, 2012 at 5:01 PM, Uros Bizjak <ubizjak@gmail.com> wrote:
>
>>> I am testing this patch.  OK for trunk if it passes all tests?
>>
>> No, force_reg will generate a pseudo, so this conversion is valid only
>> for !can_create_pseudo ().
>>
>> At least for *tls_initial_exec_x32_store, you will need a temporary to
>> split the pattern after reload.

Here is the updated patch to add can_create_pseudo.  I also changed
tls_initial_exec_x32 to take an input register operand as thread pointer.

> Please try attached patch. It simply throws away all recent
> complications w.r.t. to thread pointer and always handles TP in
> DImode.
>
> The testcase:
>
> --cut here--
> __thread int foo __attribute__ ((tls_model ("initial-exec")));
>
> void bar (int x)
> {
>  foo = x;
> }
>
> int baz (void)
> {
>  return foo;
> }
> --cut here--
>
> Now compiles to:
>
> bar:
>        movq    foo@gottpoff(%rip), %rax
>        movl    %edi, %fs:(%rax)
>        ret
>
> baz:
>        movq    foo@gottpoff(%rip), %rax
>        movl    %fs:(%rax), %eax
>        ret
>
> In effect, this always generates %fs(%rDI) and emits REX prefix before
> mov/add to satisfy brain-dead linkers.
>
> The patch is bootstrapping now on x86_64-pc-linux-gnu.
>

For

--
extern __thread char c;
extern char y;
void
ie (void)
{
  y = c;
}
--

Your patch generates:

	movl	%fs:0, %eax	
	movq	c@gottpoff(%rip), %rdx	
	movzbl	(%rax,%rdx), %edx	
	movb	%dl, y(%rip)	
	ret	

It can be optimized to:

        movq	c@gottpoff(%rip), %rax	
	movzbl	%fs:(%rax), %eax	
	movb	%al, y(%rip)	
	ret	

H.J.
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