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Re: [Patch] PR rtl-optimization/71150, guard in_class_p check with REG_P
- From: Jiong Wang <jiong dot wang at foss dot arm dot com>
- To: Uros Bizjak <ubizjak at gmail dot com>, "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>
- Cc: Vladimir Makarov <vmakarov at redhat dot com>
- Date: Tue, 17 May 2016 12:18:13 +0100
- Subject: Re: [Patch] PR rtl-optimization/71150, guard in_class_p check with REG_P
- Authentication-results: sourceware.org; auth=none
- References: <CAFULd4ZXEV-6cSyX1TFisLkocRSYR6dNk1=7L6SyG-AMcgX5rQ at mail dot gmail dot com> <CAFULd4ZBSCLVKKQoFNajYruxwVsmtV8R_jk6xkxKq=SvMM8LwA at mail dot gmail dot com>
On 17/05/16 11:23, Uros Bizjak wrote:
On Tue, May 17, 2016 at 12:17 PM, Uros Bizjak <ubizjak@gmail.com> wrote:
Hello!
This bug is introduced by my commit r236181 where the inner rtx of
SUBREG haven't been checked while it should as "in_class_p" only
works with REG, and SUBREG_REG is actually not always REG. If REG_P
check failed, then we should fall back to normal code patch. The
following simple testcase for x86 can reproduce this bug.
diff --git a/gcc/lra-constraints.c b/gcc/lra-constraints.c
index 56ab5b4..e4e6c8c 100644
--- a/gcc/lra-constraints.c
+++ b/gcc/lra-constraints.c
@@ -1317,7 +1317,8 @@ process_addr_reg (rtx *loc, bool check_only_p, rtx_insn **before, rtx_insn **aft
register, and this normally will be a subreg which should be reloaded
as a whole. This is particularly likely to be triggered when
-fno-split-wide-types specified. */
- if (in_class_p (reg, cl, &new_class)
+ if (!REG_P (reg)
+ || in_class_p (reg, cl, &new_class)
|| GET_MODE_SIZE (mode) <= GET_MODE_SIZE (ptr_mode))
loc = &SUBREG_REG (*loc);
Why not check SUBREG_P instead of !REG_P?
Or, alternatively:
if ((REG_P && !in_class_p (reg, ...))
|| GET_MODE_SIZE ...)
Which is IMO much more readable.
Thanks for review.
I think your proposed rewrite will be the following,
if (!(REG_P (reg) && !in_class_p (reg, cl, &new_class))
|| GET_MODE_SIZE (mode) <= GET_MODE_SIZE (ptr_mode))
I feel the original code is easier to understand.
The check logic is composed of three conditions, in a pre-requisite order,
if one condition is true then reload the inner rtx, otherwise reload the
whole subreg.
if (!REG_P (reg)
|| in_class_p (reg, cl, &new_class)
|| GET_MODE_SIZE (mode) <= GET_MODE_SIZE (ptr_mode))
loc = &SUBREG_REG (*loc);
Uros.