Re: PR79697: Delete calls to strdup, strndup, realloc if there is no lhs

[Prathamesh Kulkarni]

On 25 February 2017 at 14:43, Marc Glisse <marc.gli...@inria.fr> wrote:
> On Sat, 25 Feb 2017, Prathamesh Kulkarni wrote:
>
>> Hi,
>> The attached patch deletes calls to strdup, strndup if it's
>> return-value is unused,
>> and same for realloc if the first arg is NULL.
>> Bootstrap+tested on x86_64-unknown-linux-gnu.
>> OK for GCC 8 ?
>
>
> Instead of specializing realloc(0,*) wherever we can perform the same
> optimization as with malloc, wouldn't it be better to optimize:
> realloc(0,n) -> malloc(n)
> and let the malloc optimizations happen?
Thanks for the suggestions. In the attached patch, realloc (0, n) is
folded to malloc (n).
Bootstrap+test in progress on x86_64-unknown-linux-gnu.
Does the patch look OK ?

Thanks,
Prathamesh
>
> (realloc(p,0)->free(p) is more tricky because of the return value, like
> malloc(0))
>
> --
> Marc Glisse

diff --git a/gcc/gimple-fold.c b/gcc/gimple-fold.c
index a75dd91..e6eceea 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:;
     }
 
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr79697.c 
b/gcc/testsuite/gcc.dg/tree-ssa/pr79697.c
new file mode 100644
index 0000000..8219289
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr79697.c
@@ -0,0 +1,21 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-gimple -fdump-tree-cddce-details" } */
+
+void f(void)
+{
+  __builtin_strdup ("abc");
+}
+
+void g(void)
+{
+  __builtin_strndup ("abc", 3);
+}
+
+void h(void)
+{
+  __builtin_realloc (0, 10);
+}
+
+/* { 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" } } */
diff --git a/gcc/tree-ssa-dce.c b/gcc/tree-ssa-dce.c
index 5ebe57b..4225c3c 100644
--- a/gcc/tree-ssa-dce.c
+++ b/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:;