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

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 8a787163b5b694ab8d4e00026b934b830565ae9c..a20cee3f317a7414b5533e974732892ebb3b1965 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -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

diff --git a/gcc/cse.c b/gcc/cse.c
index cffa553b5257f0eebcd70bc8fb400b616737469d..dba85f1891c9d701b62965d2b3c636e242583e7c 100644 (file)
--- a/gcc/cse.c
+++ b/gcc/cse.c
@@ -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
 

diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index f2049367945447864a4eb50c680011d7c1d326ad..f7024a74579cf2c09cc80f4f23bb0df62412b91f 100644 (file)
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -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

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 128a5f7f8d7d52475428b962f1557d4f16d1fe0f..be4cb12635b36d148b75a8c2b9040b6365b1eec7 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -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

diff --git a/gcc/testsuite/g++.dg/pr49847.C b/gcc/testsuite/g++.dg/pr49847.C
new file mode 100644 (file)
index 0000000..b047713
--- /dev/null
+++ b/gcc/testsuite/g++.dg/pr49847.C
@@ -0,0 +1,7 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fnon-call-exceptions" } */
+int f (float g)
+{
+  try { return g >= 0; }
+  catch (...) {}
+}