[PATCH, rtl-optimization]: FIX PR 36111

["Uros Bizjak" <ubizjak at gmail dot com>]

Hello!

>From gcse.c, try_replace_reg (), we enter validate_src_group () with
following arguments:

insn:
(insn 8 20 0 3 pr36111.c:14 (parallel [
            (set (mem/s/c:SI (plus:SI (reg/f:SI 60)
                        (reg:SI 3 bx)) [3 main_arena.lock+0 S4 A32])
                (asm_operands/v:SI ("") ("=m") 0 [
                        (mem/s/c:SI (plus:SI (reg/f:SI 60)
                                (reg:SI 3 bx)) [3 main_arena.lock+0 S4 A32])
                    ]
                     [
                        (asm_input:SI ("m") 0)
                    ] 1741))
            (clobber (reg:QI 18 fpsr))
            (clobber (reg:QI 17 flags))
        ]) -1 (expr_list:REG_DEAD (reg/f:SI 58)
        (expr_list:REG_UNUSED (reg:QI 18 fpsr)
            (expr_list:REG_UNUSED (reg:QI 17 flags)
                (nil)))))

from:
(reg/f:SI 60)

to:
(const:SI (unspec:SI [
            (symbol_ref:SI ("main_arena") [flags 0x2] <var_decl
0xb7cc9000 main_arena>)
        ] 1))


Please note two (reg 60) pseudos inside the first element of (insn 8)
parallel that we are about to replace. note_uses () loops over all
elements of a parallel RTX and calls validate_replace_src_1 () that
passes arguments to validate_replace_rtx_1 (). We start with:

            (set (mem/s/c:SI (plus:SI (reg/f:SI 60)
                        (reg:SI 3 bx)) [3 main_arena.lock+0 S4 A32])
                (asm_operands/v:SI ("") ("=m") 0 [
                        (mem/s/c:SI (plus:SI (reg/f:SI 60)
                                (reg:SI 3 bx)) [3 main_arena.lock+0 S4 A32])
                    ]
                     [
                        (asm_input:SI ("m") 0)
                    ] 1741))


Here is the problem:

When validate_replace_rtx_1 () loops over its arguments, it
substitutes both instances of (reg 60) pseudo. Following the
individual replacement, compilation enters

  if (SWAPPABLE_OPERANDS_P (x)
      && swap_commutative_operands_p (XEXP (x, 0), XEXP (x, 1)))
    {
      validate_unshare_change (object, loc,
			       gen_rtx_fmt_ee (COMMUTATIVE_ARITH_P (x) ? code
					       : swap_condition (code),
					       GET_MODE (x), XEXP (x, 1),
					       XEXP (x, 0)), 1);

and here we generate new RTL expression that directly references XEXP
(x, 0) in order to create canonical RTX from from just created
expression with substituted operand:

(plus:SI (const:SI (unspec:SI [
                (symbol_ref:SI ("main_arena") [flags 0x2] <var_decl
0xb7d15000 main_arena>)
            ] 1))
    (reg:SI 3 bx))

This canonical RTX looks like:

(plus:SI (reg:SI 3 bx)
    (const:SI (unspec:SI [
                (symbol_ref:SI ("main_arena") [flags 0x2] <var_decl
0xb7d15000 main_arena>)
            ] 1)))


Since this happens for both pseudos that reference (reg 60), invalid
shared RTX is created.

The solution is to mark generated RTX for unsharing.

Attached patch implement this solution.

2008-05-09  Uros Bizjak  <ubizjak@gmail.com>

	PR rtl-optimization/36111
	* recog.c (validate_replace_rtx_1): Unshare new RTL expression
	that was created for swappable operands.

testsuite/ChangeLog:

2008-05-09  Uros Bizjak  <ubizjak@gmail.com>

	PR rtl-optimization/36111
	* gcc.dg/pr36111.c: New test.

The patch was regression tested on i686-pc-linux-gnu and in addition
to fixing attached testcase, it also fixes all sse3-* -O2 -fpic
failures, found at [1].

OK for mainline?

[1] http://gcc.gnu.org/ml/gcc-testresults/2008-05/msg01014.html

Uros.

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