So this is a patch that makes skipping unreachable code when
doing elimination possible. Previously interesting interactions
with tail-merging made this impossible, now I seem to have
figured a way around this.
Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.
With this more elaborate stmt folding during elimination might
be in reach.
Richard.
2017-05-10 Richard Biener <rguent...@suse.de>
* tree-ssa-pre.c (eliminate_dom_walker::before_dom_children):
Skip unreachable blocks and destinations.
(eliminate): Move stmt removal and fixup ...
(fini_eliminate): ... here. Skip inserted exprs.
(pass_pre::execute): Move fini_pre after fini_eliminate.
* tree-ssa-tailmerge.c: Include tree-cfgcleanup.h.
(tail_merge_optimize): Run cleanup_tree_cfg if requested by
PRE to get rid of dead code that has invalid SSA form and
split critical edges again.
Index: gcc/tree-ssa-pre.c
===================================================================
--- gcc/tree-ssa-pre.c (revision 247831)
+++ gcc/tree-ssa-pre.c (working copy)
@@ -4196,9 +4196,14 @@ eliminate_dom_walker::before_dom_childre
/* Mark new bb. */
el_avail_stack.safe_push (NULL_TREE);
- /* ??? If we do nothing for unreachable blocks then this will confuse
- tailmerging. Eventually we can reduce its reliance on SCCVN now
- that we fully copy/constant-propagate (most) things. */
+ /* Skip unreachable blocks marked unreachable during the SCCVN domwalk. */
+ edge_iterator ei;
+ edge e;
+ FOR_EACH_EDGE (e, ei, b->preds)
+ if (e->flags & EDGE_EXECUTABLE)
+ break;
+ if (! e)
+ return NULL;
for (gphi_iterator gsi = gsi_start_phis (b); !gsi_end_p (gsi);)
{
@@ -4695,10 +4700,8 @@ eliminate_dom_walker::before_dom_childre
}
/* Replace destination PHI arguments. */
- edge_iterator ei;
- edge e;
FOR_EACH_EDGE (e, ei, b->succs)
- {
+ if (e->flags & EDGE_EXECUTABLE)
for (gphi_iterator gsi = gsi_start_phis (e->dest);
!gsi_end_p (gsi);
gsi_next (&gsi))
@@ -4717,7 +4720,6 @@ eliminate_dom_walker::before_dom_childre
gimple_set_plf (SSA_NAME_DEF_STMT (sprime), NECESSARY, true);
}
}
- }
return NULL;
}
@@ -4743,9 +4745,6 @@ eliminate_dom_walker::after_dom_children
static unsigned int
eliminate (bool do_pre)
{
- gimple_stmt_iterator gsi;
- gimple *stmt;
-
need_eh_cleanup = BITMAP_ALLOC (NULL);
need_ab_cleanup = BITMAP_ALLOC (NULL);
@@ -4761,6 +4760,18 @@ eliminate (bool do_pre)
el_avail.release ();
el_avail_stack.release ();
+ return el_todo;
+}
+
+/* Perform CFG cleanups made necessary by elimination. */
+
+static unsigned
+fini_eliminate (void)
+{
+ gimple_stmt_iterator gsi;
+ gimple *stmt;
+ unsigned todo = 0;
+
/* We cannot remove stmts during BB walk, especially not release SSA
names there as this confuses the VN machinery. The stmts ending
up in el_to_remove are either stores or simple copies.
@@ -4782,8 +4793,9 @@ eliminate (bool do_pre)
lhs = gimple_get_lhs (stmt);
if (inserted_exprs
- && TREE_CODE (lhs) == SSA_NAME)
- bitmap_clear_bit (inserted_exprs, SSA_NAME_VERSION (lhs));
+ && TREE_CODE (lhs) == SSA_NAME
+ && bitmap_bit_p (inserted_exprs, SSA_NAME_VERSION (lhs)))
+ continue;
gsi = gsi_for_stmt (stmt);
if (gimple_code (stmt) == GIMPLE_PHI)
@@ -4800,7 +4812,7 @@ eliminate (bool do_pre)
}
/* Removing a stmt may expose a forwarder block. */
- el_todo |= TODO_cleanup_cfg;
+ todo |= TODO_cleanup_cfg;
}
el_to_remove.release ();
@@ -4819,18 +4831,10 @@ eliminate (bool do_pre)
}
if (fixup_noreturn_call (stmt))
- el_todo |= TODO_cleanup_cfg;
+ todo |= TODO_cleanup_cfg;
}
el_to_fixup.release ();
- return el_todo;
-}
-
-/* Perform CFG cleanups made necessary by elimination. */
-
-static unsigned
-fini_eliminate (void)
-{
bool do_eh_cleanup = !bitmap_empty_p (need_eh_cleanup);
bool do_ab_cleanup = !bitmap_empty_p (need_ab_cleanup);
@@ -4844,8 +4848,8 @@ fini_eliminate (void)
BITMAP_FREE (need_ab_cleanup);
if (do_eh_cleanup || do_ab_cleanup)
- return TODO_cleanup_cfg;
- return 0;
+ todo |= TODO_cleanup_cfg;
+ return todo;
}
/* Borrow a bit of tree-ssa-dce.c for the moment.
@@ -5110,8 +5114,8 @@ pass_pre::execute (function *fun)
remove_dead_inserted_code ();
scev_finalize ();
- fini_pre ();
todo |= fini_eliminate ();
+ fini_pre ();
loop_optimizer_finalize ();
/* Restore SSA info before tail-merging as that resets it as well. */
Index: gcc/tree-ssa-tail-merge.c
===================================================================
--- gcc/tree-ssa-tail-merge.c (revision 247831)
+++ gcc/tree-ssa-tail-merge.c (working copy)
@@ -205,6 +205,7 @@ along with GCC; see the file COPYING3.
#include "tree-ssa-sccvn.h"
#include "cfgloop.h"
#include "tree-eh.h"
+#include "tree-cfgcleanup.h"
/* Describes a group of bbs with the same successors. The successor bbs are
cached in succs, and the successor edge flags are cached in succ_flags.
@@ -1717,6 +1718,16 @@ tail_merge_optimize (unsigned int todo)
timevar_push (TV_TREE_TAIL_MERGE);
+ /* We enter from PRE which has critical edges split. Elimination
+ does not process trivially dead code so cleanup the CFG if we
+ are told so. And re-split critical edges then. */
+ if (todo & TODO_cleanup_cfg)
+ {
+ cleanup_tree_cfg ();
+ todo &= ~TODO_cleanup_cfg;
+ split_critical_edges ();
+ }
+
if (!dom_info_available_p (CDI_DOMINATORS))
{
/* PRE can leave us with unreachable blocks, remove them now. */
