re PR tree-optimization/79697 (unused realloc(0, n) not eliminated)

2017-04-29  Prathamesh Kulkarni  <prathamesh.kulkarni@linaro.org>

	PR tree-optimization/79697
	* tree-ssa-dce.c (mark_stmt_if_obviously_necessary): Check if callee
	is BUILT_IN_STRDUP, BUILT_IN_STRNDUP, BUILT_IN_REALLOC.
	(propagate_necessity): Check if def_callee is BUILT_IN_STRDUP or
	BUILT_IN_STRNDUP.
	* gimple-fold.c (gimple_fold_builtin_realloc): New function.
	(gimple_fold_builtin): Call gimple_fold_builtin_realloc.

testsuite/
	* gcc.dg/tree-ssa/pr79697.c: New test.

From-SVN: r247407

1 files changed, 25 insertions, 0 deletions

diff --git a/gcc/gimple-fold.c b/gcc/gimple-fold.c
index a6a958c..5ebdcdf 100644
--- a/gcc/gimple-fold.c
+++ b/gcc/gimple-fold.c
@@ -3251,6 +3251,28 @@ gimple_fold_builtin_acc_on_device (gimple_stmt_iterator *gsi, tree arg0)
   return true;
 }
 
+/* Fold realloc (0, n) -> malloc (n).  */
+
+static bool
+gimple_fold_builtin_realloc (gimple_stmt_iterator *gsi)
+{
+  gimple *stmt = gsi_stmt (*gsi);
+  tree arg = gimple_call_arg (stmt, 0);
+  tree size = gimple_call_arg (stmt, 1);
+
+  if (operand_equal_p (arg, null_pointer_node, 0))
+    {
+      tree fn_malloc = builtin_decl_implicit (BUILT_IN_MALLOC);
+      if (fn_malloc)
+	{
+	  gcall *repl = gimple_build_call (fn_malloc, 1, size);
+	  replace_call_with_call_and_fold (gsi, repl);
+	  return true;
+	}
+    }
+  return false;
+}
+
 /* Fold the non-target builtin at *GSI and return whether any simplification
    was made.  */
 
@@ -3409,6 +3431,9 @@ gimple_fold_builtin (gimple_stmt_iterator *gsi)
     case BUILT_IN_ACC_ON_DEVICE:
       return gimple_fold_builtin_acc_on_device (gsi,
 						gimple_call_arg (stmt, 0));
+    case BUILT_IN_REALLOC:
+      return gimple_fold_builtin_realloc (gsi);
+
     default:;
     }