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[PATCH] Fix promotion of const local arrays to static storage


Hi,

The fix for PR38615 indirectly broke the promotion of const local arrays
to static storage in many cases.  The commit in question, r143570, made
it so that only arrays that don't potentially escape from the scope in
which they're defined (i.e. arrays for which TREE_ADDRESSABLE is 0) are
candidates for the promotion to static storage.

The problem is that both the C and C++ frontends contain ancient code
(dating back to 1994) that sets the TREE_ADDRESSABLE bit on arrays
indexed by non-constant or out-of-range indices.  As a result, const
arrays that are indexed by non-constant or out-of-range values are no
longer candidates for promotion to static storage following the fix to
PR38615, because their TREE_ADDRESSABLE bit will always be set.
Consequently, array promotion is essentially broken for a large class of
C and C++ code.  E.g. this simple example is no longer a candidate for
promotion:

    int
    foo (int i)
    {
      const int x[] = { 1, 2, 3 };
      return x[i]; /* non-constant index */
    }

This patch removes the ancient code that is responsible for dubiously
setting the TREE_ADDRESSABLE bit on arrays indexed by non-constant or
out-of-range values.  I don't think that this code is necessary or
useful anymore.  Bootstrapped and regtested on x86_64-unknown-linux-gnu,
OK for trunk?

2014-08-18  Patrick Palka  <ppalka@gcc.gnu.org>

	* c-typeck.c (build_array_ref): Don't mark arrays indexed by
	non-constant or out-of-range values as addressable.

2014-08-18  Patrick Palka  <ppalka@gcc.gnu.org>

	* typeck.c (build_array_ref): Don't mark arrays indexed by
	non-constant or out-of-range values as addressable.

2014-08-18  Patrick Palka  <ppalka@gcc.gnu.org>

	* g++.dg/opt/static4.C: Check for static promotion.
	* g++.dg/opt/static7.C: New test.
	* gcc.dg/static1.c: New test.
---
 gcc/c/c-typeck.c                   | 23 -----------------------
 gcc/cp/typeck.c                    | 25 -------------------------
 gcc/testsuite/g++.dg/opt/static4.C |  4 ++++
 gcc/testsuite/g++.dg/opt/static7.C | 12 ++++++++++++
 gcc/testsuite/gcc.dg/static1.c     | 12 ++++++++++++
 5 files changed, 28 insertions(+), 48 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/opt/static7.C
 create mode 100644 gcc/testsuite/gcc.dg/static1.c

diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c
index e6745be..022ff8d 100644
--- a/gcc/c/c-typeck.c
+++ b/gcc/c/c-typeck.c
@@ -2487,29 +2487,6 @@ build_array_ref (location_t loc, tree array, tree index)
     {
       tree rval, type;
 
-      /* An array that is indexed by a non-constant
-	 cannot be stored in a register; we must be able to do
-	 address arithmetic on its address.
-	 Likewise an array of elements of variable size.  */
-      if (TREE_CODE (index) != INTEGER_CST
-	  || (COMPLETE_TYPE_P (TREE_TYPE (TREE_TYPE (array)))
-	      && TREE_CODE (TYPE_SIZE (TREE_TYPE (TREE_TYPE (array)))) != INTEGER_CST))
-	{
-	  if (!c_mark_addressable (array))
-	    return error_mark_node;
-	}
-      /* An array that is indexed by a constant value which is not within
-	 the array bounds cannot be stored in a register either; because we
-	 would get a crash in store_bit_field/extract_bit_field when trying
-	 to access a non-existent part of the register.  */
-      if (TREE_CODE (index) == INTEGER_CST
-	  && TYPE_DOMAIN (TREE_TYPE (array))
-	  && !int_fits_type_p (index, TYPE_DOMAIN (TREE_TYPE (array))))
-	{
-	  if (!c_mark_addressable (array))
-	    return error_mark_node;
-	}
-
       if (pedantic || warn_c90_c99_compat)
 	{
 	  tree foo = array;
diff --git a/gcc/cp/typeck.c b/gcc/cp/typeck.c
index fa3283d..6dd056d 100644
--- a/gcc/cp/typeck.c
+++ b/gcc/cp/typeck.c
@@ -3112,31 +3112,6 @@ cp_build_array_ref (location_t loc, tree array, tree idx,
 	 pointer arithmetic.)  */
       idx = cp_perform_integral_promotions (idx, complain);
 
-      /* An array that is indexed by a non-constant
-	 cannot be stored in a register; we must be able to do
-	 address arithmetic on its address.
-	 Likewise an array of elements of variable size.  */
-      if (TREE_CODE (idx) != INTEGER_CST
-	  || (COMPLETE_TYPE_P (TREE_TYPE (TREE_TYPE (array)))
-	      && (TREE_CODE (TYPE_SIZE (TREE_TYPE (TREE_TYPE (array))))
-		  != INTEGER_CST)))
-	{
-	  if (!cxx_mark_addressable (array))
-	    return error_mark_node;
-	}
-
-      /* An array that is indexed by a constant value which is not within
-	 the array bounds cannot be stored in a register either; because we
-	 would get a crash in store_bit_field/extract_bit_field when trying
-	 to access a non-existent part of the register.  */
-      if (TREE_CODE (idx) == INTEGER_CST
-	  && TYPE_DOMAIN (TREE_TYPE (array))
-	  && ! int_fits_type_p (idx, TYPE_DOMAIN (TREE_TYPE (array))))
-	{
-	  if (!cxx_mark_addressable (array))
-	    return error_mark_node;
-	}
-
       if (!lvalue_p (array))
 	{
 	  if (complain & tf_error)
diff --git a/gcc/testsuite/g++.dg/opt/static4.C b/gcc/testsuite/g++.dg/opt/static4.C
index 87e11b0..bae22c9 100644
--- a/gcc/testsuite/g++.dg/opt/static4.C
+++ b/gcc/testsuite/g++.dg/opt/static4.C
@@ -3,6 +3,7 @@
 // if they are promoted to static storage.
 
 // { dg-do compile }
+// { dg-options "-fdump-tree-gimple" }
 
 int g(int i) { 
   if (i<1) { 
@@ -13,3 +14,6 @@ int g(int i) {
     return x[i]; 
   } 
 } 
+
+// { dg-final { scan-tree-dump-times "static const int" 2 "gimple" } }
+// { dg-final { cleanup-tree-dump "gimple" } }
diff --git a/gcc/testsuite/g++.dg/opt/static7.C b/gcc/testsuite/g++.dg/opt/static7.C
new file mode 100644
index 0000000..2a9f678
--- /dev/null
+++ b/gcc/testsuite/g++.dg/opt/static7.C
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-fdump-tree-gimple" } */
+
+int
+foo (int x)
+{
+  const int y[] = { 1, 2, 3 };
+  return y[x];
+}
+
+/* { dg-final { scan-tree-dump "static const int" "gimple" } } */
+/* { dg-final { cleanup-tree-dump "gimple" } } */
diff --git a/gcc/testsuite/gcc.dg/static1.c b/gcc/testsuite/gcc.dg/static1.c
new file mode 100644
index 0000000..2a9f678
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/static1.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-fdump-tree-gimple" } */
+
+int
+foo (int x)
+{
+  const int y[] = { 1, 2, 3 };
+  return y[x];
+}
+
+/* { dg-final { scan-tree-dump "static const int" "gimple" } } */
+/* { dg-final { cleanup-tree-dump "gimple" } } */
-- 
2.1.0


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