arm.c (arm_legitimize_reload_address): Explain why plus_constant is not used.

2013-10-02  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>

	* config/arm/arm.c (arm_legitimize_reload_address): Explain why
	plus_constant is not used.

From-SVN: r203106

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index e0b30a373ebaf90061db128e937cb263dd337194..7dc504bbf3b0b4cc4ce35c9dbcda8a03b7474e65 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2013-10-02  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
+
+       * config/arm/arm.c (arm_legitimize_reload_address): Explain why
+       plus_constant is not used.
+
 2013-10-01  Wei Mi  <wmi@google.com>
 
        * config/i386/x86-tune.def (DEF_TUNE): Remove

diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index cc3eec767aed80562553d2c53e5ef64c5f4e6af8..f0a7deae67d1ea98c94b59036118a7047d6d7e4f 100644 (file)
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -7015,7 +7015,11 @@ 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)),