[ was: Re: [RFC] ldist: Recognize rawmemchr loop patterns ]
On 1/31/22 16:00, Richard Biener wrote:
I'm running into PR56888 (
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56888 ) on nvptx due to
this, f.i. in gcc/testsuite/gcc.c-torture/execute/builtins/strlen.c,
where gcc/testsuite/gcc.c-torture/execute/builtins/lib/strlen.c contains
a strlen function, with a strlen loop, which is transformed by
pass_loop_distribution into a __builtin_strlen, which is then expanded
into a strlen call, creating a self-recursive function. [ And on nvptx,
that happens to result in a compilation failure, which is how I found
this. ]
According to this (
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56888#c21 ) comment:
...
-fno-tree-loop-distribute-patterns is the reliable way to not
transform loops into library calls.
...
Then should we have something along the lines of:
...
$ git diff
diff --git a/gcc/tree-loop-distribution.c b/gcc/tree-loop-distribution.c
index 6fe59cd56855..9a211d30cd7e 100644
--- a/gcc/tree-loop-distribution.c
+++ b/gcc/tree-loop-distribution.c
@@ -3683,7 +3683,11 @@ loop_distribution::transform_reduction_loop
&& TYPE_PRECISION (ptr_type_node) >= 32)
|| (TYPE_OVERFLOW_UNDEFINED (reduction_var_type)
&& TYPE_PRECISION (reduction_var_type) <=
TYPE_PRECISION (sizetype)))
- && builtin_decl_implicit (BUILT_IN_STRLEN))
+ && builtin_decl_implicit (BUILT_IN_STRLEN)
+ && flag_tree_loop_distribute_patterns)
generate_strlen_builtin (loop, reduction_var, load_iv.base,
reduction_iv.base, loc);
else if (direct_optab_handler (rawmemchr_optab, TYPE_MODE
(load_type))
...
?
Or is the comment no longer valid?
It is still valid - and yes, I think we need to guard it with this flag
but please do it in the caller to transform_reduction_loop.
Done.
Ok for trunk?
Thanks,
- Tom
[ldist] Don't add lib calls with -fno-tree-loop-distribute-patterns
As mentioned in PR56888 comment 21:
...
-fno-tree-loop-distribute-patterns is the reliable way to not
transform loops into library calls.
...
However, since commit 6f966f06146 ("ldist: Recognize strlen and rawmemchr like
loops") a strlen or rawmemchr library call may be introduced by ldist.
This caused regressions in testcases
gcc.c-torture/execute/builtins/strlen{,-2,-3}.c for nvptx.
Fix this by not calling transform_reduction_loop from
loop_distribution::execute for -fno-tree-loop-distribute-patterns.
Tested regressing test-cases as well as gcc.dg/tree-ssa/ldist-*.c on
nvptx.
gcc/ChangeLog:
2022-01-31 Tom de Vries <tdevr...@suse.de>
* tree-loop-distribution.cc (generate_reduction_builtin_1): Check for
-ftree-loop-distribute-patterns.
(loop_distribution::execute): Don't call transform_reduction_loop for
-fno-tree-loop-distribute-patterns.
gcc/testsuite/ChangeLog:
2022-01-31 Tom de Vries <tdevr...@suse.de>
* gcc.dg/tree-ssa/ldist-strlen-4.c: New test.
---
gcc/testsuite/gcc.dg/tree-ssa/ldist-strlen-4.c | 17 +++++++++++++++++
gcc/tree-loop-distribution.cc | 5 ++++-
2 files changed, 21 insertions(+), 1 deletion(-)
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ldist-strlen-4.c b/gcc/testsuite/gcc.dg/tree-ssa/ldist-strlen-4.c
new file mode 100644
index 000000000000..eafb37e84fc3
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ldist-strlen-4.c
@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -ftree-loop-distribution -fno-tree-loop-distribute-patterns -fdump-tree-ldist-details" } */
+/* { dg-final { scan-tree-dump-not "generated strlen" "ldist" } } */
+
+/* Copied from gcc/testsuite/gcc.c-torture/execute/builtins/lib/strlen.c. */
+
+__SIZE_TYPE__
+foo (const char *s)
+{
+ __SIZE_TYPE__ i;
+
+ i = 0;
+ while (s[i] != 0)
+ i++;
+
+ return i;
+}
diff --git a/gcc/tree-loop-distribution.cc b/gcc/tree-loop-distribution.cc
index 6fe59cd56855..c7b428572636 100644
--- a/gcc/tree-loop-distribution.cc
+++ b/gcc/tree-loop-distribution.cc
@@ -3290,6 +3290,8 @@ generate_reduction_builtin_1 (loop_p loop, gimple_seq &seq,
tree reduction_var_old, tree reduction_var_new,
const char *info, machine_mode load_mode)
{
+ gcc_assert (flag_tree_loop_distribute_patterns);
+
/* Place new statements before LOOP. */
gimple_stmt_iterator gsi = gsi_last_bb (loop_preheader_edge (loop)->src);
gsi_insert_seq_after (&gsi, seq, GSI_CONTINUE_LINKING);
@@ -3773,7 +3775,8 @@ loop_distribution::execute (function *fun)
if (niters == NULL_TREE || niters == chrec_dont_know)
{
datarefs_vec.create (20);
- if (transform_reduction_loop (loop))
+ if (flag_tree_loop_distribute_patterns
+ && transform_reduction_loop (loop))
{
changed = true;
loops_to_be_destroyed.safe_push (loop);
