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[PATCH][ARM][committed] Add comment in arm_legitimize_reload_address to discourage use of plus_constant
- From: Kyrill Tkachov <kyrylo dot tkachov at arm dot com>
- To: GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Wed, 02 Oct 2013 11:06:09 +0100
- Subject: [PATCH][ARM][committed] Add comment in arm_legitimize_reload_address to discourage use of plus_constant
- Authentication-results: sourceware.org; auth=none
Hi all,
I've committed the attached patch to make it mode clear why we use gen_rtx_PLUS
instead of plus_constant in that particular instance.
Committed as obvious with r203106.
Kyrill
2013-10-02 Kyrylo Tkachov <kyrylo.tkachov@arm.com>
* config/arm/arm.c (arm_legitimize_reload_address): Explain why
plus_constant is not used.diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index e23e29a..2f1e0b8 100644
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -7547,7 +7547,11 @@ arm_legitimize_reload_address (rtx *p,
return false;
/* Reload the high part into a base reg; leave the low part
- in the mem. */
+ in the mem.
+ Note that replacing this gen_rtx_PLUS with plus_constant is
+ wrong in this case because we rely on the
+ (plus (plus reg c1) c2) structure being preserved so that
+ XEXP (*p, 0) in push_reload below uses the correct term. */
*p = gen_rtx_PLUS (GET_MODE (*p),
gen_rtx_PLUS (GET_MODE (*p), XEXP (*p, 0),
GEN_INT (high)),