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[PR44610] don't delegitimize MEM from base without offset
- From: Alexandre Oliva <aoliva at redhat dot com>
- To: gcc-patches at gcc dot gnu dot org
- Date: Thu, 24 Jun 2010 00:47:21 -0300
- Subject: [PR44610] don't delegitimize MEM from base without offset
Interesting bug... All words of a multi-word variable ended up mapped
to the same VALUE during cselib in var-tracking, and then their location
was set to the same REG, that held only the first word.
Problem was that we were initializing the variable within a loop, from
an array element that lived in memory and varied per iteration of the
loop. This means the MEM_OFFSETs couldn't be set: they weren't
constant.
Turns out that some recently-added code that attempted to simplify MEMs
to something more palatable than complex expressions involving frame,
stack or GOT pointers, mistook the absence of an offset for a zero
offset. So, because of this delegitimization, each of the words loaded
into part of the variable was regarded by cselib as a MEM referencing
the first word of the array. Oops.
This patch prevents the delegitimization when the offset is unknown, so
that we don't get bogus equivalences.
Regstrapped on x86_64-linux-gnu, i686-linux-gnu and ia64-linux-gnu.
Ok for trunk?
for gcc/ChangeLog
from Alexandre Oliva <aoliva@redhat.com>
PR debug/44610
* simplify-rtx.c (delegitimize_mem_from_attrs): Don't use a base
address if the offset is unknown.
Index: gcc/simplify-rtx.c
===================================================================
--- gcc/simplify-rtx.c.orig 2010-06-23 01:15:14.000000000 -0300
+++ gcc/simplify-rtx.c 2010-06-23 01:20:21.000000000 -0300
@@ -208,10 +208,11 @@ avoid_constant_pool_reference (rtx x)
rtx
delegitimize_mem_from_attrs (rtx x)
{
+ /* MEMs without MEM_OFFSETs may have been offset, so we can't just
+ use their base addresses as equivalent. */
if (MEM_P (x)
&& MEM_EXPR (x)
- && (!MEM_OFFSET (x)
- || GET_CODE (MEM_OFFSET (x)) == CONST_INT))
+ && MEM_OFFSET (x))
{
tree decl = MEM_EXPR (x);
enum machine_mode mode = GET_MODE (x);
@@ -264,8 +265,7 @@ delegitimize_mem_from_attrs (rtx x)
{
rtx newx;
- if (MEM_OFFSET (x))
- offset += INTVAL (MEM_OFFSET (x));
+ offset += INTVAL (MEM_OFFSET (x));
newx = DECL_RTL (decl);
--
Alexandre Oliva, freedom fighter http://FSFLA.org/~lxoliva/
You must be the change you wish to see in the world. -- Gandhi
Be Free! -- http://FSFLA.org/ FSF Latin America board member
Free Software Evangelist Red Hat Brazil Compiler Engineer