[PATCH, PR50527] Don't assume alignment of vla-related allocas.

[Tom de Vries]

Richard,

I got a patch for PR50527.

The patch prevents the alignment of vla-related allocas to be set to
BIGGEST_ALIGNMENT in ccp. The alignment may turn out smaller after folding
the alloca.

Bootstrapped and regtested on x86_64.

OK for trunk?

Thanks,
- Tom

2011-09-27  Tom de Vries  <t...@codesourcery.com>

        * tree-ssa-ccp.c (evaluate_stmt): Don't assume alignment for vla-related
        allocas.

        * gcc.dg/pr50527.c: New test.

Index: gcc/tree-ssa-ccp.c
===================================================================
--- gcc/tree-ssa-ccp.c (revision 179210)
+++ gcc/tree-ssa-ccp.c (working copy)
@@ -1632,6 +1632,8 @@ evaluate_stmt (gimple stmt)
 	      break;
 
 	    case BUILT_IN_ALLOCA:
+	      if (gimple_call_alloca_for_var_p (stmt))
+		break;
 	      val.lattice_val = CONSTANT;
 	      val.value = build_int_cst (TREE_TYPE (gimple_get_lhs (stmt)), 0);
 	      val.mask = shwi_to_double_int
Index: gcc/testsuite/gcc.dg/pr50527.c
===================================================================
--- /dev/null (new file)
+++ gcc/testsuite/gcc.dg/pr50527.c (revision 0)
@@ -0,0 +1,46 @@
+/* { dg-do run } */
+/* { dg-options "-Os --param large-stack-frame=30" } */
+
+extern void abort (void);
+
+void __attribute__((noinline)) 
+bar (char *a)
+{
+}
+
+void __attribute__((noinline)) 
+foo (char *a, int b)
+{
+}
+
+void __attribute__((noinline))
+test_align (char *p, int aligned, unsigned int mask)
+{
+  int p_aligned = ((unsigned long int)p & mask) == 0;
+  if (aligned != p_aligned)
+    abort ();
+}
+
+int
+main ()
+{
+  const int kIterations = 4;
+  char results[kIterations];
+  int i;
+  unsigned int mask;
+
+  mask = 0xf;
+  test_align (results, ((unsigned long int)results & mask) == 0, mask);
+  mask = 0x7;
+  test_align (results, ((unsigned long int)results & mask) == 0, mask);
+  mask = 0x3;
+  test_align (results, ((unsigned long int)results & mask) == 0, mask);
+  mask = 0x1;
+  test_align (results, ((unsigned long int)results & mask) == 0, mask);
+
+  bar (results);
+  for (i = 0; i < kIterations; i++)
+    foo ("%d ", results[i]);
+
+  return 0;
+}