re PR rtl-optimization/51374 ([avr] insn combine reorders volatile memory accesses)

gcc/
	PR rtl-optimization/51374
	* combine.c (can_combine_p): Don't allow volatile_refs_p insns
	to cross other volatile_refs_p insns.

gcc/testsuite/
	PR rtl-optimization/51374
	* testsuite/gcc.target/avr/torture/pr51374-1.c: New.

From-SVN: r183796

gcc/ChangeLog

+2012-02-01  Georg-Johann Lay  <avr@gjlay.de>
+
+	PR rtl-optimization/51374
+	* combine.c (can_combine_p): Don't allow volatile_refs_p insns
+	to cross other volatile_refs_p insns.
+
 2012-02-01  Richard Guenther  <rguenther@suse.de>
 
 	* doc/invoke.texi (fno-inline): Clarify documentation.

gcc/combine.c

@@ -1700,6 +1700,7 @@ can_combine_p (rtx insn, rtx i3, rtx pred ATTRIBUTE_UNUSED,
   rtx link;
 #endif
   bool all_adjacent = true;
+  int (*is_volatile_p) (const_rtx);
 
   if (succ)
     {
@@ -1948,11 +1949,17 @@ can_combine_p (rtx insn, rtx i3, rtx pred ATTRIBUTE_UNUSED,
       && REG_P (dest) && REGNO (dest) < FIRST_PSEUDO_REGISTER)
     return 0;
 
-  /* If there are any volatile insns between INSN and I3, reject, because
-     they might affect machine state.  */
+  /* If INSN contains volatile references (specifically volatile MEMs),
+     we cannot combine across any other volatile references.
+     Even if INSN doesn't contain volatile references, any intervening
+     volatile insn might affect machine state.  */
 
+  is_volatile_p = volatile_refs_p (PATTERN (insn))
+    ? volatile_refs_p
+    : volatile_insn_p;
+    
   for (p = NEXT_INSN (insn); p != i3; p = NEXT_INSN (p))
-    if (INSN_P (p) && p != succ && p != succ2 && volatile_insn_p (PATTERN (p)))
+    if (INSN_P (p) && p != succ && p != succ2 && is_volatile_p (PATTERN (p)))
       return 0;
 
   /* If INSN contains an autoincrement or autodecrement, make sure that

gcc/testsuite/ChangeLog

+2012-02-01  Georg-Johann Lay  <avr@gjlay.de>
+
+	PR rtl-optimization/51374
+	* testsuite/gcc.target/avr/torture/pr51374-1.c: New.
+
 2012-01-31  Tobias Burnus  <burnus@net-b.de>
 
 	PR fortran/52024

gcc/testsuite/gcc.target/avr/torture/pr51374-1.c

+/* PR rtl-optimization/51374 */
+/* { dg-do compile } */
+
+void vector_18 (void)
+{
+    extern char slot;
+    unsigned char status = (*(volatile unsigned char*) 0x2B);
+    unsigned char data   = (*(volatile unsigned char*) 0x2C);
+
+    if (status & 0x10)
+        slot = 0;
+}
+
+/* { dg-final { scan-assembler-not "\tsbic " } } */