Patchwork [i386] : Fix PR 53853, FAIL: g++.dg/other/pr53811.C -std=gnu++* (internal compiler error) with -fPIC

login
register
mail settings
Submitter Uros Bizjak
Date July 6, 2012, 9:58 a.m.
Message ID <CAFULd4asXHjDMrVVD9heQbxnp0B81w+K02mw534mjMRRMpY3pw@mail.gmail.com>
Download mbox | patch
Permalink /patch/169402/
State New
Headers show

Comments

Uros Bizjak - July 6, 2012, 9:58 a.m.
Hello!

Symbol references are not legitimate sibcall operands for
-mcmodel=large, so have to be moved to registers (using movabs).
Unfortunately, moving symbol references for CM_LARGE_PIC requires PIC
fixup which by default generates Pmode pseudos. When generating thunk
in x86_output_mi_thunk, we are already past reload time, so pseudos
are not allowed.

The solution is to call legitimize_pic_address with hard temporary
Pmode register in advance, to avoid situations that would lead to
generation of pseudo registers in emit_move_insn. Patched gcc
generates:

        .set    .LTHUNK0,_ZN1D4foo2Ev
        .p2align 4,,15
        .globl  _ZThn16_N1D4foo2Ev
        .type   _ZThn16_N1D4foo2Ev, @function
_ZThn16_N1D4foo2Ev:
.LFB15:
        .cfi_startproc
        subq    $16, %rdi
        movabsq $.LTHUNK0@GOTOFF, %r10
        addq    %rbx, %r10
        jmp     *%r10
        .cfi_endproc
.LFE15:
        .size   _ZThn16_N1D4foo2Ev, .-_ZThn16_N1D4foo2Ev

which is the same as when calling static local functions with
-mcmodel=large -fPIC.

2012-07-06  Uros Bizjak  <ubizjak@gmail.com>

	PR target/53811
	* config/i386/i386.c (x86_output_mi_thunk): For CM_LARGE_PIC model,
	emit PIC sequence for fnaddr symbol reference in advance.

Tested on x86_64-pc-linux-gnu {,-m32} and by testing various runtime
tests in testsuite/g++.dg/inherit with "-mcmodel=large -fPIC".

Committed to mainline SVN, will backport to 4.7.

Uros.

Patch

Index: config/i386/i386.c
===================================================================
--- config/i386/i386.c	(revision 189310)
+++ config/i386/i386.c	(working copy)
@@ -33057,6 +33057,10 @@  x86_output_mi_thunk (FILE *file,
     emit_jump_insn (gen_indirect_jump (fnaddr));
   else
     {
+      if (ix86_cmodel == CM_LARGE_PIC && SYMBOLIC_CONST (fnaddr))
+	fnaddr = legitimize_pic_address (fnaddr,
+					 gen_rtx_REG (Pmode, tmp_regno));
+
       if (!sibcall_insn_operand (fnaddr, word_mode))
 	{
 	  tmp = gen_rtx_REG (word_mode, tmp_regno);