Hi,
when turning a tail-recursive call into a loop, the tail-call pass
creates a phi node for each gimple_reg function parameter that has any
use at all, even when the value passed to the original call is the same
as the received one, when it is the parameter's default definition.
This results in a redundant phi node in which one argument is the
default definition and all others are the LHS of the same phi node. See
the Bugzilla entry for an example. These phi nodes in turn confuses
ipa-prop.c which cannot skip them and may not create a pass-through jump
function when it should.
Fixed by the following patch which just adds a bitmap to remember where
there are non-default-defs passed to a tail-recursive call and then
creates phi nodes only for such parameters. It has passed bootstrap and
testing on x86_64-linux.
OK for trunk?
Martin
2019-08-28 Martin Jambor <mjam...@suse.cz>
tree-optimization/91579
* tree-tailcall.c (tailr_non_ddef_args): New variable.
(find_tail_calls): Allocate tailr_non_ddef_args and set its bits as
appropriate.
(arg_needs_copy_p): New parameter idx. Also check
tailr_non_ddef_args.
(tree_optimize_tail_calls_1): Free tailr_non_ddef_args.
testsuite/
* gcc.dg/tree-ssa/pr91579.c: New test.
---
gcc/testsuite/gcc.dg/tree-ssa/pr91579.c | 22 ++++++++++++++
gcc/tree-tailcall.c | 38 +++++++++++++++++++------
2 files changed, 52 insertions(+), 8 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr91579.c
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr91579.c
b/gcc/testsuite/gcc.dg/tree-ssa/pr91579.c
new file mode 100644
index 00000000000..ee752be1a85
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr91579.c
@@ -0,0 +1,22 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-tailr1" } */
+
+typedef long unsigned int size_t;
+typedef int (*compare_t)(const void *, const void *);
+
+int partition (void *base, size_t nmemb, size_t size, compare_t cmp);
+
+void
+my_qsort (void *base, size_t nmemb, size_t size, compare_t cmp)
+{
+ int pt;
+ if (nmemb > 1)
+ {
+ pt = partition (base, nmemb, size, cmp);
+ my_qsort (base, pt + 1, size, cmp);
+ my_qsort ((void*)((char*) base + (pt + 1) * size),
+ nmemb - pt - 1, size, cmp);
+ }
+}
+
+/* { dg-final { scan-tree-dump-not "cmp\[^\r\n\]*PHI" "tailr1" } } */
diff --git a/gcc/tree-tailcall.c b/gcc/tree-tailcall.c
index a4b563efd73..23d60f492da 100644
--- a/gcc/tree-tailcall.c
+++ b/gcc/tree-tailcall.c
@@ -126,6 +126,13 @@ struct tailcall
accumulator. */
static tree m_acc, a_acc;
+/* Bitmap with a bit for each function parameter which is set to true if in a
+ tail-recursion we pass to the actual argument something else than the
+ default definition of the corresponding formal parameter. It has no meaning
+ for non-gimple-register parameters. */
+
+static bitmap tailr_non_ddef_args;
+
static bool optimize_tail_call (struct tailcall *, bool);
static void eliminate_tail_call (struct tailcall *);
@@ -727,6 +734,17 @@ find_tail_calls (basic_block bb, struct tailcall **ret)
gimple_stmt_iterator mgsi = gsi_for_stmt (stmt);
gsi_move_before (&mgsi, &gsi);
}
+ if (!tailr_non_ddef_args)
+ tailr_non_ddef_args = BITMAP_ALLOC (NULL);
+ for (param = DECL_ARGUMENTS (current_function_decl), idx = 0;
+ param;
+ param = DECL_CHAIN (param), idx++)
+ {
+ tree arg = gimple_call_arg (call, idx);
+ if (is_gimple_reg (param)
+ && (arg != ssa_default_def (cfun, param)))
+ bitmap_set_bit (tailr_non_ddef_args, idx);
+ }
}
nw = XNEW (struct tailcall);
@@ -905,11 +923,11 @@ decrease_profile (basic_block bb, profile_count count)
}
}
-/* Returns true if argument PARAM of the tail recursive call needs to be copied
- when the call is eliminated. */
+/* Returns true if PARAM, which is the IDX-th argument of the tail recursively
+ called function, needs to be copied when the call is eliminated. */
static bool
-arg_needs_copy_p (tree param)
+arg_needs_copy_p (tree param, unsigned idx)
{
tree def;
@@ -918,7 +936,7 @@ arg_needs_copy_p (tree param)
/* Parameters that are only defined but never used need not be copied. */
def = ssa_default_def (cfun, param);
- if (!def)
+ if (!def || !bitmap_bit_p (tailr_non_ddef_args, idx))
return false;
return true;
@@ -1005,7 +1023,7 @@ eliminate_tail_call (struct tailcall *t)
param;
param = DECL_CHAIN (param), idx++)
{
- if (!arg_needs_copy_p (param))
+ if (!arg_needs_copy_p (param, idx))
continue;
arg = gimple_call_arg (stmt, idx);
@@ -1139,10 +1157,11 @@ tree_optimize_tail_calls_1 (bool opt_tailcalls)
split_edge (single_succ_edge (ENTRY_BLOCK_PTR_FOR_FN (cfun)));
/* Copy the args if needed. */
- for (param = DECL_ARGUMENTS (current_function_decl);
+ unsigned idx;
+ for (param = DECL_ARGUMENTS (current_function_decl), idx = 0;
param;
- param = DECL_CHAIN (param))
- if (arg_needs_copy_p (param))
+ param = DECL_CHAIN (param), idx++)
+ if (arg_needs_copy_p (param, idx))
{
tree name = ssa_default_def (cfun, param);
tree new_name = make_ssa_name (param, SSA_NAME_DEF_STMT (name));
@@ -1206,6 +1225,9 @@ tree_optimize_tail_calls_1 (bool opt_tailcalls)
if (phis_constructed)
mark_virtual_operands_for_renaming (cfun);
+ if (tailr_non_ddef_args)
+ BITMAP_FREE (tailr_non_ddef_args);
+
if (changed)
return TODO_cleanup_cfg | TODO_update_ssa_only_virtuals;
return 0;
--
2.22.0
