re PR rtl-optimization/78812 (Wrong code generation due to hoisting memory load across function call)

PR tree-optimizatin/78812
	* rtl.h (contains_mem_rtx_p): Prototype.
	* ifcvt.c (containts_mem_rtx_p): Move from here to...
	* rtlanal.c (contains_mem_rtx_p): Here and remvoe static linkage.
	* gcse.c (prune_expressions): Use contains_mem_rtx_p to discover
	and prune MEMs that are not at the toplevel of a SET_SRC rtx.  Look
	through ZERO_EXTEND and SIGN_EXTEND when trying to avoid pruning
	MEMs.

	PR tree-optimization/78812
	* g++.dg/torture/pr78812.C: New test.

From-SVN: r244093

gcc/ChangeLog

@@ -1,3 +1,14 @@
+2017-01-04  Jeff Law  <law@redhat.com>
+
+	PR tree-optimizatin/78812
+	* rtl.h (contains_mem_rtx_p): Prototype.
+	* ifcvt.c (containts_mem_rtx_p): Move from here to...
+	* rtlanal.c (contains_mem_rtx_p): Here and remvoe static linkage.
+	* gcse.c (prune_expressions): Use contains_mem_rtx_p to discover
+	and prune MEMs that are not at the toplevel of a SET_SRC rtx.  Look
+	through ZERO_EXTEND and SIGN_EXTEND when trying to avoid pruning
+	MEMs.
+
 2017-01-04  Alexandre Oliva <aoliva@redhat.com>
 
 	* input.c (assert_char_at_range): Default-initialize

gcc/gcse.c

@@ -1709,7 +1709,7 @@ prune_expressions (bool pre_p)
 	      continue;
 	    }
 
-	  if (!pre_p && MEM_P (expr->expr))
+	  if (!pre_p && contains_mem_rtx_p (expr->expr))
 	    /* Note memory references that can be clobbered by a call.
 	       We do not split abnormal edges in hoisting, so would
 	       a memory reference get hoisted along an abnormal edge,
@@ -1717,15 +1717,28 @@ prune_expressions (bool pre_p)
 	       constant memory references can be hoisted along abnormal
 	       edges.  */
 	    {
-	      if (GET_CODE (XEXP (expr->expr, 0)) == SYMBOL_REF
+	      rtx x = expr->expr;
-		  && CONSTANT_POOL_ADDRESS_P (XEXP (expr->expr, 0)))
-		continue;
 
-	      if (MEM_READONLY_P (expr->expr)
+	      /* Common cases where we might find the MEM which may allow us
-		  && !MEM_VOLATILE_P (expr->expr)
+		 to avoid pruning the expression.  */
-		  && MEM_NOTRAP_P (expr->expr))
+	      while (GET_CODE (x) == ZERO_EXTEND || GET_CODE (x) == SIGN_EXTEND)
-		/* Constant memory reference, e.g., a PIC address.  */
+		x = XEXP (x, 0);
-		continue;
+
+	      /* If we found the MEM, go ahead and look at it to see if it has
+		 properties that allow us to avoid pruning its expression out
+		 of the tables.  */
+	      if (MEM_P (x))
+		{
+		  if (GET_CODE (XEXP (x, 0)) == SYMBOL_REF
+		      && CONSTANT_POOL_ADDRESS_P (XEXP (x, 0)))
+		    continue;
+
+		  if (MEM_READONLY_P (x)
+		      && !MEM_VOLATILE_P (x)
+		      && MEM_NOTRAP_P (x))
+		    /* Constant memory reference, e.g., a PIC address.  */
+		    continue;
+		}
 
 	      /* ??? Optimally, we would use interprocedural alias
 		 analysis to determine if this mem is actually killed

gcc/ifcvt.c

@@ -3010,19 +3010,6 @@ noce_operand_ok (const_rtx op)
   return ! may_trap_p (op);
 }
 
-/* Return true if X contains a MEM subrtx.  */
-
-static bool
-contains_mem_rtx_p (rtx x)
-{
-  subrtx_iterator::array_type array;
-  FOR_EACH_SUBRTX (iter, array, x, ALL)
-    if (MEM_P (*iter))
-      return true;
-
-  return false;
-}
-
 /* Return true iff basic block TEST_BB is valid for noce if-conversion.
    The condition used in this if-conversion is in COND.
    In practice, check that TEST_BB ends with a single set

gcc/rtl.h

@@ -3090,6 +3090,7 @@ extern bool rtx_referenced_p (const_rtx, const_rtx);
 extern bool tablejump_p (const rtx_insn *, rtx_insn **, rtx_jump_table_data **);
 extern int computed_jump_p (const rtx_insn *);
 extern bool tls_referenced_p (const_rtx);
+extern bool contains_mem_rtx_p (rtx x);
 
 /* Overload for refers_to_regno_p for checking a single register.  */
 inline bool

gcc/rtlanal.c

@@ -685,6 +685,19 @@ rtx_addr_can_trap_p (const_rtx x)
   return rtx_addr_can_trap_p_1 (x, 0, 0, VOIDmode, false);
 }
 
+/* Return true if X contains a MEM subrtx.  */
+
+bool
+contains_mem_rtx_p (rtx x)
+{
+  subrtx_iterator::array_type array;
+  FOR_EACH_SUBRTX (iter, array, x, ALL)
+    if (MEM_P (*iter))
+      return true;
+
+  return false;
+}
+
 /* Return true if X is an address that is known to not be zero.  */
 
 bool

gcc/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2017-01-04  Jeff Law  <law@redhat.com>
+
+	PR tree-optimization/78812
+	* g++.dg/torture/pr78812.C: New test.
+
 2017-01-04  Michael Meissner  <meissner@linux.vnet.ibm.com>
 
 	PR target/71977

gcc/testsuite/g++.dg/torture/pr78812.C

@@ -0,0 +1,24 @@
+// { dg-do run } 
+// { dg-options "-fpic" { target fpic } }
+
+struct T
+{
+  bool a;
+  T () : a (false) {}
+  ~T () { if (!a) __builtin_abort (); }
+};
+
+__attribute__((noinline))
+void
+test (T &x)
+{
+  x.a = true;
+}
+
+int
+main ()
+{
+  T T;
+  test (T);
+}
+