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re PR rtl-optimization/49847 (NULL deref in fold_rtx (prev_insn_cc0 == NULL)) 

PR rtl-optimization/49847
	* cse.c (fold_rtx) Handle case where cc0 setter and cc0 user
	are in different blocks.
	* doc/tm.texi (Condition Code Status): Update documention for
	relative locations of cc0-setter and cc0-user.

	 PR rtl-optimization/49847
	 * g++.dg/pr49847.C: New test.

Co-Authored-By: Jeff Law <law@redhat.com>

From-SVN: r208203
This commit is contained in:
Mikael Pettersson 2014-02-27 20:02:18 +01:00 committed by Jeff Law
parent b076556843
commit 728acca06e
5 changed files with 50 additions and 5 deletions
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9
gcc/ChangeLog
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@ -1,3 +1,12 @@
2014-02-27 Mikael Pettersson <mikpe@it.uu.se>
Jeff Law <law@redhat.com>
PR rtl-optimization/49847
* cse.c (fold_rtx) Handle case where cc0 setter and cc0 user
are in different blocks.
* doc/tm.texi (Condition Code Status): Update documention for
relative locations of cc0-setter and cc0-user.
2014-02-27 Vladimir Makarov <vmakarov@redhat.com>
PR target/59222

24
gcc/cse.c
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@ -3199,9 +3199,27 @@ fold_rtx (rtx x, rtx insn)
#ifdef HAVE_cc0
case CC0:
folded_arg = prev_insn_cc0;
mode_arg = prev_insn_cc0_mode;
const_arg = equiv_constant (folded_arg);
/* The cc0-user and cc0-setter may be in different blocks if
the cc0-setter potentially traps. In that case PREV_INSN_CC0
will have been cleared as we exited the block with the
setter.
While we could potentially track cc0 in this case, it just
doesn't seem to be worth it given that cc0 targets are not
terribly common or important these days and trapping math
is rarely used. The combination of those two conditions
necessary to trip this situation is exceedingly rare in the
real world. */
if (!prev_insn_cc0)
{
const_arg = NULL_RTX;
}
else
{
folded_arg = prev_insn_cc0;
mode_arg = prev_insn_cc0_mode;
const_arg = equiv_constant (folded_arg);
}
break;
#endif

9
gcc/doc/tm.texi
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@ -5900,8 +5900,13 @@ most instructions do not affect it. The latter category includes
most RISC machines.
The implicit clobbering poses a strong restriction on the placement of
the definition and use of the condition code, which need to be in adjacent
insns for machines using @code{(cc0)}. This can prevent important
the definition and use of the condition code. In the past the definition
and use were always adjacent. However, recent changes to support trapping
arithmatic may result in the definition and user being in different blocks.
Thus, there may be a @code{NOTE_INSN_BASIC_BLOCK} between them. Additionally,
the definition may be the source of exception handling edges.
These restrictions can prevent important
optimizations on some machines. For example, on the IBM RS/6000, there
is a delay for taken branches unless the condition code register is set
three instructions earlier than the conditional branch. The instruction

6
gcc/testsuite/ChangeLog
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@ -1,3 +1,9 @@
2014-02-27 Mikael Pettersson <mikpe@it.uu.se>
Jeff Law <law@redhat.com>
PR rtl-optimization/49847
* g++.dg/pr49847.C: New test.
2014-02-27 Marek Polacek <polacek@redhat.com>
PR middle-end/59223

7
gcc/testsuite/g++.dg/pr49847.C Normal file
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@ -0,0 +1,7 @@
/* { dg-do compile } */
/* { dg-options "-O -fnon-call-exceptions" } */
int f (float g)
{
try { return g >= 0; }
catch (...) {}
}