[PATCH] Improve build_simple_mem_ref_loc (PR middle-end/83185)

[Jakub Jelinek <jakub@redhat.com>]

Hi!

This PR is about forwprop propagating:
  _17 = __builtin_alloca_with_align (_16, 256);
  _18 = _17 + 32;
  __builtin___asan_alloca_poison (_18, _8);
  _7 = &*_18[4];
  __builtin_va_start (_7, 0);
to:
  _17 = __builtin_alloca_with_align (_16, 256);
  _18 = _17 + 32;
  __builtin___asan_alloca_poison (_18, _8);
  _7 = &MEM[(struct [0:D.2257][1] *)_17 + 32B][4];
  __builtin_va_start (_7, 0);
which is something the verifiers allow and then backend VA_START
handling calling build_simple_mem_ref_loc on the ADDR_EXPR it got.
get_addr_base_and_unit_offset only looks through a MEM_REF if it
has ADDR_EXPR as the first operand, which is not the case here, so nothing
sums up the 96 offset from the [4] ARRAY_REF with the extra 32 from the
MEM_REF.

Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux, ok for
trunk?

2017-11-29  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/83185
	* tree.c (build_simple_mem_ref_loc): Handle
	get_addr_base_and_unit_offset returning a MEM_REF.

	* gcc.dg/asan/pr83185.c: New test.

--- gcc/tree.c.jj	2017-11-28 12:11:38.000000000 +0100
+++ gcc/tree.c	2017-11-28 17:22:01.800939050 +0100
@@ -4692,7 +4692,13 @@ build_simple_mem_ref_loc (location_t loc
     {
       ptr = get_addr_base_and_unit_offset (TREE_OPERAND (ptr, 0), &offset);
       gcc_assert (ptr);
-      ptr = build_fold_addr_expr (ptr);
+      if (TREE_CODE (ptr) == MEM_REF)
+	{
+	  offset += mem_ref_offset (ptr).to_short_addr ();
+	  ptr = TREE_OPERAND (ptr, 0);
+	}
+      else
+	ptr = build_fold_addr_expr (ptr);
       gcc_assert (is_gimple_reg (ptr) || is_gimple_min_invariant (ptr));
     }
   tem = build2 (MEM_REF, TREE_TYPE (ptype),
--- gcc/testsuite/gcc.dg/asan/pr83185.c.jj	2017-11-28 17:24:15.540329283 +0100
+++ gcc/testsuite/gcc.dg/asan/pr83185.c	2017-11-28 17:24:19.851277394 +0100
@@ -0,0 +1,14 @@
+/* PR middle-end/83185 */
+/* { dg-do compile } */
+
+#include <stdarg.h>
+
+int bar (void);
+
+void
+foo (int i, ...)
+{
+  va_list aps[bar()];
+  va_start (aps[4], i);
+  va_end (aps[4]);
+}

	Jakub