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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: Alex Velenko <Alex dot Velenko at arm dot com>, "Bin.Cheng" <amker dot cheng at gmail dot com>
Cc: Felix Yang <fei dot yang0953 at gmail dot com>, "Yangfei (Felix)" <felix dot yang at huawei dot com>, Marcus Shawcroft <Marcus dot Shawcroft at arm dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>, "vmakarov at redhat dot com" <vmakarov at redhat dot com>
Date: Fri, 13 Feb 2015 16:18:36 -0700
Subject: Re: [PATCH IRA] update_equiv_regs fails to set EQUIV reg-note for pseudo with more than one definition
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On 02/12/15 05:40, Alex Velenko wrote:

On 09/02/15 23:32, Jeff Law wrote:

On 02/03/15 20:03, Bin.Cheng wrote:

I looked into the test and can confirm the previous compilation is
correct.
The cover letter of this patch said IRA mis-handled REQ_EQUIV before,
but in this case it is REG_EQUAL that is lost.  The full dump (without
this patch) after IRA is like:

Right, but a REG_EQUIV is generated based on the incoming REG_EQUAL
notes in the insn stream.  Basically update_equiv_regs will scan insn
stream and some REG_EQUAL notes will be promoted to REG_EQUIV notes.


Hi Jeff,
Do I understand you correctly, that REG_EQUAL notes should not be
generated in IRA pass, because some of them may get promoted to
REG_EQUIV? Or is there any other reason register r110 should not get
REG_EQUAL note? Previously, register r110 was getting REG_EQUAL, not
REG_EQUIV note.

The reason r110 can not get a REG_EQUIV note is because there aremultiple insns that set r110 to different values.

The equivalency created by a REG_EQUIV note has to be valid at everypoint within the function. Thus for any pseudo that holds > 1 distinctvalue within a function there can be no valid REG_EQUIV notes on theassignments to that pseudo.




jeff

References:
- Re: Re: [PATCH IRA] update_equiv_regs fails to set EQUIV reg-note for pseudo with more than one definition
  - From: Alex Velenko
- Re: [PATCH IRA] update_equiv_regs fails to set EQUIV reg-note for pseudo with more than one definition
  - From: Jeff Law
- Re: [PATCH IRA] update_equiv_regs fails to set EQUIV reg-note for pseudo with more than one definition
  - From: Bin.Cheng
- Re: [PATCH IRA] update_equiv_regs fails to set EQUIV reg-note for pseudo with more than one definition
  - From: Jeff Law
- Re: [PATCH IRA] update_equiv_regs fails to set EQUIV reg-note for pseudo with more than one definition
  - From: Bin.Cheng
- Re: [PATCH IRA] update_equiv_regs fails to set EQUIV reg-note for pseudo with more than one definition
  - From: Jeff Law
- Re: [PATCH IRA] update_equiv_regs fails to set EQUIV reg-note for pseudo with more than one definition
  - From: Alex Velenko

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