[PATCH] Do not fold addressable operands of "m" into non-addressable (PR inline-asm/50571, take 2)

[Jakub Jelinek <jakub at redhat dot com>]

Hi!

On Fri, Sep 30, 2011 at 10:34:28AM +0200, Richard Guenther wrote:
> Hmm, I don't think this change is ok.  We rely on maybe_fold_reference
> to re-fold mem-refs to valid gimple form (from propagating say
> &a.b.c to MEM[p, 4] which first gives the invalid MEM[&a.b.c, 4] and
> then the folding changes this to MEM[&a, 12]).  You need to preserve that
> and only disable constant folding.
> 
> Thus I suggest to add a parameter to maybe_fold_reference that says
> whether to try constant folding (we already have is_lhs, so why not
> use that?)

So like this instead?

2011-09-30  Jakub Jelinek  <jakub@redhat.com>

	PR inline-asm/50571
	* gimple-fold.c (fold_stmt_1) <case GIMPLE_ASM>: If
	input constraints allow mem and not reg, pass true instead of
	false as second argument to maybe_fold_reference.

	* gcc.dg/pr50571.c: New test.

--- gcc/gimple-fold.c.jj	2011-09-29 14:25:46.000000000 +0200
+++ gcc/gimple-fold.c	2011-09-30 10:54:10.000000000 +0200
@@ -1201,28 +1201,45 @@ fold_stmt_1 (gimple_stmt_iterator *gsi, 
 
     case GIMPLE_ASM:
       /* Fold *& in asm operands.  */
-      for (i = 0; i < gimple_asm_noutputs (stmt); ++i)
-	{
-	  tree link = gimple_asm_output_op (stmt, i);
-	  tree op = TREE_VALUE (link);
-	  if (REFERENCE_CLASS_P (op)
-	      && (op = maybe_fold_reference (op, true)) != NULL_TREE)
-	    {
-	      TREE_VALUE (link) = op;
-	      changed = true;
-	    }
-	}
-      for (i = 0; i < gimple_asm_ninputs (stmt); ++i)
-	{
-	  tree link = gimple_asm_input_op (stmt, i);
-	  tree op = TREE_VALUE (link);
-	  if (REFERENCE_CLASS_P (op)
-	      && (op = maybe_fold_reference (op, false)) != NULL_TREE)
-	    {
-	      TREE_VALUE (link) = op;
-	      changed = true;
-	    }
-	}
+      {
+	size_t noutputs;
+	const char **oconstraints;
+	const char *constraint;
+	bool allows_mem, allows_reg;
+
+	noutputs = gimple_asm_noutputs (stmt);
+	oconstraints = XALLOCAVEC (const char *, noutputs);
+
+	for (i = 0; i < gimple_asm_noutputs (stmt); ++i)
+	  {
+	    tree link = gimple_asm_output_op (stmt, i);
+	    tree op = TREE_VALUE (link);
+	    oconstraints[i]
+	      = TREE_STRING_POINTER (TREE_VALUE (TREE_PURPOSE (link)));
+	    if (REFERENCE_CLASS_P (op)
+		&& (op = maybe_fold_reference (op, true)) != NULL_TREE)
+	      {
+		TREE_VALUE (link) = op;
+		changed = true;
+	      }
+	  }
+	for (i = 0; i < gimple_asm_ninputs (stmt); ++i)
+	  {
+	    tree link = gimple_asm_input_op (stmt, i);
+	    tree op = TREE_VALUE (link);
+	    constraint
+	      = TREE_STRING_POINTER (TREE_VALUE (TREE_PURPOSE (link)));
+	    parse_input_constraint (&constraint, 0, 0, noutputs, 0,
+				    oconstraints, &allows_mem, &allows_reg);
+	    if (REFERENCE_CLASS_P (op)
+		&& (op = maybe_fold_reference (op, !allows_reg && allows_mem))
+		   != NULL_TREE)
+	      {
+		TREE_VALUE (link) = op;
+		changed = true;
+	      }
+	  }
+      }
       break;
 
     case GIMPLE_DEBUG:
--- gcc/testsuite/gcc.dg/pr50571.c.jj	2011-09-29 21:28:05.000000000 +0200
+++ gcc/testsuite/gcc.dg/pr50571.c	2011-09-29 21:30:08.000000000 +0200
@@ -0,0 +1,11 @@
+/* PR inline-asm/50571 */
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+static const int var[4] = { 1, 2, 3, 4 };
+
+void
+foo (void)
+{
+  __asm volatile ("" : : "m" (*(int *) var));
+}


	Jakub