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Re: [PATCH IRA] update_equiv_regs fails to set EQUIV reg-note for pseudo with more than one definition
- From: Jeff Law <law at redhat dot com>
- To: Felix Yang <fei dot yang0953 at gmail dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>, vmakarov at redhat dot com
- Date: Mon, 22 Sep 2014 12:40:44 -0600
- Subject: Re: [PATCH IRA] update_equiv_regs fails to set EQUIV reg-note for pseudo with more than one definition
- Authentication-results: sourceware.org; auth=none
- References: <CAFc0fxz3Fdr9rgLscjTzZm0PoBn53y028tQU4=U0BXQ0kY6+KA at mail dot gmail dot com>
On 09/22/14 08:40, Felix Yang wrote:
Hi,
I find that update_equiv_regs in ira.c sets the wrong EQUIV
reg-note for pseudo with more than one definiton in certain situation.
Here is a simplified RTL snippet after this function finishs handling:
(insn 77 37 78 2 (set (reg:SI 171)
(const_int 0 [0])) ticket151.c:33 52 {movsi_internal_dsp}
(expr_list:REG_EQUAL (const_int 0 [0])
(nil)))
......
(insn 79 50 53 2 (set (mem/c:SI (reg/f:SI 136) [2 g_728+0 S4 A64])
(reg:SI 171)) ticket151.c:33 52 {movsi_internal_dsp}
(expr_list:REG_DEAD (reg:SI 171)
(nil)))
(insn 53 79 54 2 (set (mem/c:SI (reg/f:SI 162) [4 g_163+0 S4 A32])
(reg:SI 163)) 52 {movsi_internal_dsp}
(expr_list:REG_DEAD (reg:SI 163)
(expr_list:REG_DEAD (reg/f:SI 162)
(nil))))
(insn 54 53 14 2 (set (reg:SI 171)
(mem/u/c:SI (symbol_ref/u:SI ("*.LC8") [flags 0x2]) [4 S4
A32])) ticket151.c:49 52 {movsi_internal_dsp}
(expr_list:REG_EQUIV (mem/u/c:SI (symbol_ref/u:SI ("*.LC8")
[flags 0x2]) [4 S4 A32])
(expr_list:REG_EQUAL (mem/u/c:SI (symbol_ref/u:SI ("*.LC8")
[flags 0x2]) [4 S4 A32])
(nil))))
The REG_EQUIV of insn 54 is not correct as pseudo 171 is defined
in insn 77 with a differerent value.
This may causes reload replacing pseudo 171 with mem/u/c:SI
(symbol_ref/u:SI ("*.LC8"), which is wrong.
A proposed patch for this issue, please comment:
Is it possible it's the conditional just above this one that is incorrect?
if (DF_REG_DEF_COUNT (regno) != 1
&& (! note
|| rtx_varies_p (XEXP (note, 0), 0)
|| (reg_equiv[regno].replacement
&& ! rtx_equal_p (XEXP (note, 0),
reg_equiv[regno].replacement))))
{
no_equiv (dest, set, NULL);
continue;
}
ISTM the only time a multiply-set register can have a valid REG_EQUIV
note is if each and every assignment to that pseudo has the same RHS.
Jeff