2011-08-31 Tom de Vries <tom@codesourcery.com>

	PR middle-end/43513
	* Makefile.in (tree-ssa-ccp.o): Add $(PARAMS_H) to rule.
	* tree-ssa-ccp.c (params.h): Include.
	(fold_builtin_alloca_for_var): New function.
	(ccp_fold_stmt): Use fold_builtin_alloca_for_var.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@178353 138bc75d-0d04-0410-961f-82ee72b054a4

3 files changed, 69 insertions, 1 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index da9fec0088d..ad45eb4c96e 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,11 @@
+2011-08-31  Tom de Vries  <tom@codesourcery.com>
+
+	PR middle-end/43513
+	* Makefile.in (tree-ssa-ccp.o): Add $(PARAMS_H) to rule.
+	* tree-ssa-ccp.c (params.h): Include.
+	(fold_builtin_alloca_for_var): New function.
+	(ccp_fold_stmt): Use fold_builtin_alloca_for_var.
+
 2011-08-30  Uros Bizjak  <ubizjak@gmail.com>
 
 	* config/i386/i386.c (ix86_valid_target_attribute_inner_p):
diff --git a/gcc/Makefile.in b/gcc/Makefile.in
index 8679e7b961e..d5caba6c7f7 100644
--- a/gcc/Makefile.in
+++ b/gcc/Makefile.in
@@ -3154,7 +3154,7 @@ tree-call-cdce.o : tree-call-cdce.c $(CONFIG_H) $(SYSTEM_H) $(TREE_H) \
 tree-ssa-ccp.o : tree-ssa-ccp.c $(TREE_FLOW_H) $(CONFIG_H) \
    $(SYSTEM_H) $(TREE_H) $(TM_P_H) $(EXPR_H) output.h \
    $(DIAGNOSTIC_H) $(FUNCTION_H) $(TIMEVAR_H) $(TM_H) coretypes.h \
-   $(TREE_DUMP_H) $(BASIC_BLOCK_H) $(TREE_PASS_H) langhooks.h \
+   $(TREE_DUMP_H) $(BASIC_BLOCK_H) $(TREE_PASS_H) langhooks.h  $(PARAMS_H) \
    tree-ssa-propagate.h value-prof.h $(FLAGS_H) $(TARGET_H) $(DIAGNOSTIC_CORE_H) \
    $(DBGCNT_H) tree-pretty-print.h gimple-pretty-print.h gimple-fold.h
 tree-sra.o : tree-sra.c $(CONFIG_H) $(SYSTEM_H) coretypes.h alloc-pool.h \
diff --git a/gcc/tree-ssa-ccp.c b/gcc/tree-ssa-ccp.c
index 55a504ee52d..007e17dd8b6 100644
--- a/gcc/tree-ssa-ccp.c
+++ b/gcc/tree-ssa-ccp.c
@@ -133,6 +133,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "diagnostic-core.h"
 #include "dbgcnt.h"
 #include "gimple-fold.h"
+#include "params.h"
 
 
 /* Possible lattice values.  */
@@ -1684,6 +1685,51 @@ evaluate_stmt (gimple stmt)
   return val;
 }
 
+/* Detects a vla-related alloca with a constant argument.  Declares fixed-size
+   array and return the address, if found, otherwise returns NULL_TREE.  */
+
+static tree
+fold_builtin_alloca_for_var (gimple stmt)
+{
+  unsigned HOST_WIDE_INT size, threshold, n_elem;
+  tree lhs, arg, block, var, elem_type, array_type;
+  unsigned int align;
+
+  /* Get lhs.  */
+  lhs = gimple_call_lhs (stmt);
+  if (lhs == NULL_TREE)
+    return NULL_TREE;
+
+  /* Detect constant argument.  */
+  arg = get_constant_value (gimple_call_arg (stmt, 0));
+  if (arg == NULL_TREE || TREE_CODE (arg) != INTEGER_CST
+      || !host_integerp (arg, 1))
+    return NULL_TREE;
+  size = TREE_INT_CST_LOW (arg);
+
+  /* Heuristic: don't fold large vlas.  */
+  threshold = (unsigned HOST_WIDE_INT)PARAM_VALUE (PARAM_LARGE_STACK_FRAME);
+  /* In case a vla is declared at function scope, it has the same lifetime as a
+     declared array, so we allow a larger size.  */
+  block = gimple_block (stmt);
+  if (!(cfun->after_inlining
+        && TREE_CODE (BLOCK_SUPERCONTEXT (block)) == FUNCTION_DECL))
+    threshold /= 10;
+  if (size > threshold)
+    return NULL_TREE;
+
+  /* Declare array.  */
+  elem_type = build_nonstandard_integer_type (BITS_PER_UNIT, 1);
+  n_elem = size * 8 / BITS_PER_UNIT;
+  align = MIN (size * 8, BIGGEST_ALIGNMENT);
+  array_type = build_array_type_nelts (elem_type, n_elem);
+  var = create_tmp_var (array_type, NULL);
+  DECL_ALIGN (var) = align;
+
+  /* Fold alloca to the address of the array.  */
+  return fold_convert (TREE_TYPE (lhs), build_fold_addr_expr (var));
+}
+
 /* Fold the stmt at *GSI with CCP specific information that propagating
    and regular folding does not catch.  */
 
@@ -1752,6 +1798,20 @@ ccp_fold_stmt (gimple_stmt_iterator *gsi)
 	if (gimple_call_internal_p (stmt))
 	  return false;
 
+        /* The heuristic of fold_builtin_alloca_for_var differs before and after
+           inlining, so we don't require the arg to be changed into a constant
+           for folding, but just to be constant.  */
+        if (gimple_call_alloca_for_var_p (stmt))
+          {
+            tree new_rhs = fold_builtin_alloca_for_var (stmt);
+            bool res;
+            if (new_rhs == NULL_TREE)
+              return false;
+            res = update_call_from_tree (gsi, new_rhs);
+            gcc_assert (res);
+            return true;
+          }
+
 	/* Propagate into the call arguments.  Compared to replace_uses_in
 	   this can use the argument slot types for type verification
 	   instead of the current argument type.  We also can safely