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

gcc/ChangeLog

+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.
+
 2017-04-28  Martin Sebor  <msebor@redhat.com>
 
 	PR tree-optimization/80523

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:;
     }
 

gcc/testsuite/ChangeLog

+2017-04-29  Prathamesh Kulkarni  <prathamesh.kulkarni@linaro.org>
+
+	PR tree-optimization/79697
+	* gcc.dg/tree-ssa/pr79697.c: New test.
+
 2017-04-29  Tom de Vries  <tom@codesourcery.com>
 
 	* gcc.dg/tree-prof/pr66295.c: Require effective target avx512f.

gcc/testsuite/gcc.dg/tree-ssa/pr79697.c

+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-gimple -fdump-tree-cddce-details -fdump-tree-optimized" } */
+
+void f(void)
+{
+  __builtin_strdup ("abc");
+}
+
+void g(void)
+{
+  __builtin_strndup ("abc", 3);
+}
+
+void h(void)
+{
+  __builtin_realloc (0, 10);
+}
+
+void k(void)
+{
+  char *p = __builtin_strdup ("abc");
+  __builtin_free (p);
+
+  char *q = __builtin_strndup ("abc", 3);
+  __builtin_free (q);
+}
+
+/* { dg-final { scan-tree-dump "Deleting : __builtin_strdup" "cddce1" } } */
+/* { dg-final { scan-tree-dump "Deleting : __builtin_strndup" "cddce1" } } */
+/* { dg-final { scan-tree-dump "__builtin_malloc" "gimple" } } */
+/* { dg-final { scan-tree-dump-not "__builtin_strdup" "optimized" } } */
+/* { dg-final { scan-tree-dump-not "__builtin_strndup" "optimized" } } */
+/* { dg-final { scan-tree-dump-not "__builtin_free" "optimized" } } */

gcc/tree-ssa-dce.c

@@ -233,6 +233,8 @@ mark_stmt_if_obviously_necessary (gimple *stmt, bool aggressive)
 	    case BUILT_IN_CALLOC:
 	    case BUILT_IN_ALLOCA:
 	    case BUILT_IN_ALLOCA_WITH_ALIGN:
+	    case BUILT_IN_STRDUP:
+	    case BUILT_IN_STRNDUP:
 	      return;
 
 	    default:;
@@ -780,7 +782,9 @@ propagate_necessity (bool aggressive)
 		  && DECL_BUILT_IN_CLASS (def_callee) == BUILT_IN_NORMAL
 		  && (DECL_FUNCTION_CODE (def_callee) == BUILT_IN_ALIGNED_ALLOC
 		      || DECL_FUNCTION_CODE (def_callee) == BUILT_IN_MALLOC
-		      || DECL_FUNCTION_CODE (def_callee) == BUILT_IN_CALLOC))
+		      || DECL_FUNCTION_CODE (def_callee) == BUILT_IN_CALLOC
+		      || DECL_FUNCTION_CODE (def_callee) == BUILT_IN_STRDUP
+		      || DECL_FUNCTION_CODE (def_callee) == BUILT_IN_STRNDUP))
 		{
 		  gimple *bounds_def_stmt;
 		  tree bounds;