On 26 February 2017 at 05:16, Martin Sebor <mse...@gmail.com> wrote:
> On 02/25/2017 11:54 AM, Prathamesh Kulkarni wrote:
>>
>> 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 ?
>
>
> Although it's not part of the bug report, I wonder if a complete
> patch should also extend the malloc/free DCE to str{,n}dup/free
> calls and eliminate pairs like these:
>
> void f (const char *s)
> {
> char *p = strdup (src);
> free (p);
> }
>
> (That seems to be just a matter of adding a couple of conditionals
> for BUILT_IN_STR{,N}DUP in propagate_necessity).
Hi Martin,
Thanks for the suggestions, I have updated the patch accordingly.
Does it look OK ?
>
> Martin
>
> PS Another optimization, though one that's most likely outside
> the scope of this patch, is to eliminate all of the following:
>
> void f (const char *s, char *s2)
> {
> char *p = strdup (s);
> strcpy (p, s2);
> free (p);
> }
>
> as is done in:
>
> void f (unsigned n, const char *s)
> {
> char *p = malloc (n);
> memcpy (p, s, n);
> free (p);
> }
>
Hmm, dse1 detects that the store to p in memcpy() is dead and deletes the call.
cddce1 then removes calls to malloc and free thus making the function empty.
It doesn't work if memcpy is replaced by strcpy:
void f (unsigned n, char *s2)
{
char *p = __builtin_malloc (n);
__builtin_strcpy (p, s2);
__builtin_free (p);
}
I suppose strcpy should be special-cased too in dse similar to memcpy ?
Thanks,
Prathamesh
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..d4f6473
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr79697.c
@@ -0,0 +1,33 @@
+/* { 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" } } */
diff --git a/gcc/tree-ssa-dce.c b/gcc/tree-ssa-dce.c
index 5ebe57b..e17659d 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:;
@@ -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;
