From patchwork Wed Jun 1 22:25:39 2011 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: introduce --param max-vartrack-expr-depth Date: Wed, 01 Jun 2011 12:25:39 -0000 From: Alexandre Oliva X-Patchwork-Id: 98284 Message-Id: To: Bernd Schmidt Cc: gcc-patches@gcc.gnu.org On Jun 1, 2011, Alexandre Oliva wrote: > On May 31, 2011, Alexandre Oliva wrote: >> On May 30, 2011, Bernd Schmidt 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)