PR middle-end/13400

	* ifcvt.c (noce_process_if_block): Disable unconditional write
	optimizations if we could introduce a store to trapping memory
	that wasn't present previously.

	* gcc.c-torture/execute/20031215-1.c: New test case.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@74663 138bc75d-0d04-0410-961f-82ee72b054a4

4 files changed, 69 insertions, 0 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index cc3def4ec09..950083c2712 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2003-12-15  Roger Sayle  <roger@eyesopen.com>
+
+	PR middle-end/13400
+	* ifcvt.c (noce_process_if_block): Disable unconditional write
+	optimizations if we could introduce a store to trapping memory
+	that wasn't present previously.
+
 2003-12-15  Kazu Hirata  <kazu@cs.umass.edu>
 
 	* system.h (DEFAULT_CALLER_SAVES): Poison.
diff --git a/gcc/ifcvt.c b/gcc/ifcvt.c
index 4a13ba2a45b..8aba0d50efc 100644
--- a/gcc/ifcvt.c
+++ b/gcc/ifcvt.c
@@ -1965,6 +1965,25 @@ noce_process_if_block (struct ce_if_block * ce_info)
       goto success;
     }
 
+  /* Disallow the "if (...) x = a;" form (with an implicit "else x = x;")
+     for most optimizations if writing to x may trap, i.e. its a memory
+     other than a static var or a stack slot.  */
+  if (! set_b
+      && GET_CODE (orig_x) == MEM
+      && ! MEM_NOTRAP_P (orig_x)
+      && rtx_addr_can_trap_p (XEXP (orig_x, 0)))
+    {
+      if (HAVE_conditional_move)
+	{
+	  if (noce_try_cmove (&if_info))
+	    goto success;
+	  if (! HAVE_conditional_execution
+	      && noce_try_cmove_arith (&if_info))
+	    goto success;
+	}
+      return FALSE;
+    }
+
   if (noce_try_move (&if_info))
     goto success;
   if (noce_try_store_flag (&if_info))
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 8862f109ff2..96c0ee8a93e 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2003-12-15  Roger Sayle  <roger@eyesopen.com>
+
+	PR middle-end/13400
+	* gcc.c-torture/execute/20031215-1.c: New test case.
+
 2003-12-15  Mark Mitchell  <mark@codesourcery.com>
 
 	PR c++/13269
diff --git a/gcc/testsuite/gcc.c-torture/execute/20031215-1.c b/gcc/testsuite/gcc.c-torture/execute/20031215-1.c
new file mode 100644
index 00000000000..d62177b2618
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/20031215-1.c
@@ -0,0 +1,38 @@
+/* PR middle-end/13400 */
+/* The following test used to fail at run-time with a write to read-only
+   memory, caused by if-conversion converting a conditional write into an
+   unconditional write.  */
+
+typedef struct {int c, l; char ch[3];} pstr;
+const pstr ao = {2, 2, "OK"};
+const pstr * const a = &ao;
+
+void test1(void)
+{
+    if (a->ch[a->l]) {
+        ((char *)a->ch)[a->l] = 0;
+    }
+}
+
+void test2(void)
+{
+    if (a->ch[a->l]) {
+        ((char *)a->ch)[a->l] = -1;
+    }
+}
+
+void test3(void)
+{
+    if (a->ch[a->l]) {
+        ((char *)a->ch)[a->l] = 1;
+    }
+}
+
+int main(void)
+{
+    test1();
+    test2();
+    test3();
+    return 0;
+}
+