On Jun 1, 2011, Alexandre Oliva <[email protected]> wrote:
> On May 31, 2011, Alexandre Oliva <[email protected]> wrote:
>> On May 30, 2011, Bernd Schmidt <[email protected]> wrote:
>>> On 05/30/2011 12:35 PM, Alexandre Oliva wrote:
>>>> One of my patches for PR 48866 regressed guality/asm-1.c on
>>>> x86_64-linux-gnu because what used to be a single complex debug value
>>>> expression became a chain of debug temps holding simpler expressions,
>>>> and this chain exceeded the default recursion depth in resolving
>>>> location expressions.
>>> What's the worst that can happen if you remove the limit altogether?
>> Exponential behavior comes to mind.
> It's unusual, but debug/pr41264-1.c exhibits it, given INT_MAX for the
> param, even though under such a (lack of) limit bootstrap doesn't go
> slower or faster, after restoring depth 5 for the reverse_op() use. As
> Jakub pointed out, that one probably shouldn't be affected by the
> parameter, as depth 5 is exactly what we want for the kind of expression
> we're looking for. With unlimited depth for that one, not even
> libiberty/md5.c compiles successfully, exhausting memory on a box with
> some 40GB of total VM (8+32).
> So I guess I'll stick with what I checked in, but keep a patch handy to
> bump the limit a little bit up and revert to 5 in reverse_op.
Such as this one...
Index: gcc/params.def
===================================================================
--- gcc/params.def.orig 2011-05-31 18:28:05.348070586 -0300
+++ gcc/params.def 2011-06-01 17:09:41.117140944 -0300
@@ -845,7 +845,7 @@ DEFPARAM (PARAM_MAX_VARTRACK_SIZE,
DEFPARAM (PARAM_MAX_VARTRACK_EXPR_DEPTH,
"max-vartrack-expr-depth",
"Max. recursion depth for expanding var tracking expressions",
- 10, 0, 0)
+ 20, 0, 0)
/* Set minimum insn uid for non-debug insns. */
Index: gcc/var-tracking.c
===================================================================
--- gcc/var-tracking.c.orig 2011-05-31 20:06:25.604477956 -0300
+++ gcc/var-tracking.c 2011-05-31 23:56:06.578450957 -0300
@@ -5288,7 +5288,7 @@ reverse_op (rtx val, const_rtx expr)
arg = XEXP (src, 1);
if (!CONST_INT_P (arg) && GET_CODE (arg) != SYMBOL_REF)
{
- arg = cselib_expand_value_rtx (arg, scratch_regs, EXPR_DEPTH);
+ arg = cselib_expand_value_rtx (arg, scratch_regs, 5);
if (arg == NULL_RTX)
return NULL_RTX;
if (!CONST_INT_P (arg) && GET_CODE (arg) != SYMBOL_REF)
--
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
