Eric Botcazou - [4.1] Fix PR rtl-optimization/30787 (original) (raw)

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• From: Eric Botcazou
• To: gcc-patches at gcc dot gnu dot org
• Date: Fri, 16 Feb 2007 21:54:15 +0100
• Subject: [4.1] Fix PR rtl-optimization/30787

This is a regression from the 3.x series of compilers present in 4.1.x on x86 and x86-64, again the old loop optimizer. When reducing the GIV associated with y->s[i] in

for (i = 0; i < x; i++) { if (y) y->s[i] += 1; }

it hoists the initial value y->s out of the loop, thus bypassing the guard.

It's a variant of

2005-12-16 Jakub Jelinek jakub@redhat.com

PR rtl-optimization/24899
* loop.c (strength_reduce): Don't reduce giv that is not always
computable and where add_val or mult_val can trap.

with an additional subtlety: the GIV is a DEST_ADDR instead of a DEST_REG so it is deemed "always computable", albeit not "always executed".

Bootstrapped/regtested on x86_64-suse-linux and applied to 4.1 branch. The change has no effect whatsoever on the 300+ preprocessed files of a C/C++/Ada bootstrap at -O2 on x86.

2007-02-16 Eric Botcazou ebotcazou@libertysurf.fr

PR rtl-optimization/30787
* loop.c (strength_reduce): Don't reduce giv that is not always
executed and where add_val or mult_val can trap.

2007-02-16 Eric Botcazou ebotcazou@libertysurf.fr

* gcc.c-torture/compile/20070216-1.c: New test.

-- Eric Botcazou

Index: loop.c

--- loop.c (revision 121990) +++ loop.c (working copy) @@ -6493,13 +6493,13 @@ strength_reduce (struct loop *loop, int v->ignore = 1; bl->all_reduced = 0; } - else if (!v->always_computable + else if (! v->always_executed && (may_trap_or_fault_p (v->add_val) || may_trap_or_fault_p (v->mult_val))) { if (loop_dump_stream) fprintf (loop_dump_stream, - "giv of insn %d: not always computable.\n", + "giv of insn %d: not always executed.\n", INSN_UID (v->insn)); v->ignore = 1; bl->all_reduced = 0;

/* PR rtl-optimization/30787 / / Testcase by Jakub Jelinek jakub@gcc.gnu.org */

struct S { int *s; };

void test (int x, struct S *y) { int i; for (i = 0; i < x; i++) { if (y) y->s[i] += 1; } }

int main (void) { test (1, (void *) 0); return 0; }

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