Another step along the path to fixing 69196. As I was investigating the
regression, one of the things that became quite clear was that we'd
greatly increased the number of PHIs and many of the PHI arguments were
constants (which in turn never coalesce and thus generate a constant
initialization).
I think this addresses the accounting issues relevant to 69196 in the
backwards (FSM) threader. I don't expect this patch in and of itself to
have any significant impact on the testcase -- it's just preparatory
work for the clamp.
Bootstrapped and regression tested on x86_64-linux-gnu. Installed on
the trunk.
Jeff
commit 5810fc48902c737b3e0ea24bd2a709edbde41ff2
Author: Jeff Law <l...@redhat.com>
Date: Tue Mar 1 14:41:35 2016 -0700
PR tree-optimization/69196
* tree-ssa-threadbackward.c (fsm_find_control_statement_thread_paths):
Do count some PHIs in the thread path against the insn count. Decrease
final statement count by one as the control statement in the last
block will get removed. Remove special cased code for handling PHIs
in the last block.
PR tree-optimization/69196
* gcc.dg/tree-ssa/vrp46.c: Twiddle threading params to keep it from
duplicating code and spoiling the expected output.
diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index b758d42..c1f2557 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,11 @@
+2016-03-01 Jeff Law <l...@redhat.com>
+
+ PR tree-optimization/69196
+ * tree-ssa-threadbackward.c (fsm_find_control_statement_thread_paths):
+ Do count some PHIs in the thread path against the insn count. Decrease
+ final statement count by one as the control statement in the last
+ block will get removed. Remove special cased code for handling PHIs
in the last block.
+
2016-03-01 Uros Bizjak <ubiz...@gmail.com>
PR target/70027
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 000ece8..ef8a987 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2016-03-01 Jeff Law <l...@redhat.com>
+
+ PR tree-optimization/69196
+ * gcc.dg/tree-ssa/vrp46.c: Twiddle threading params to keep it from
+ duplicating code and spoiling the expected output.
+
2016-03-01 Michael Meissner <meiss...@linux.vnet.ibm.com>
PR target/70033
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/vrp46.c
b/gcc/testsuite/gcc.dg/tree-ssa/vrp46.c
index 8923eb4..d3c9ed1 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/vrp46.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/vrp46.c
@@ -1,5 +1,5 @@
/* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-vrp1" } */
+/* { dg-options "-O2 -fdump-tree-vrp1 --param fsm-scale-path-blocks=1" } */
int func_81 (int);
int func_98 (int);
diff --git a/gcc/tree-ssa-threadbackward.c b/gcc/tree-ssa-threadbackward.c
index 55dbcad..3028504 100644
--- a/gcc/tree-ssa-threadbackward.c
+++ b/gcc/tree-ssa-threadbackward.c
@@ -286,6 +286,37 @@ fsm_find_control_statement_thread_paths (tree name,
break;
}
+ /* PHIs in the path will create degenerate PHIS in the
+ copied path which will then get propagated away, so
+ looking at just the duplicate path the PHIs would
+ seem unimportant.
+
+ But those PHIs, because they're assignments to objects
+ typically with lives that exist outside the thread path,
+ will tend to generate PHIs (or at least new PHI arguments)
+ at points where we leave the thread path and rejoin
+ the original blocks. So we do want to account for them.
+
+ We ignore virtual PHIs. We also ignore cases where BB
+ has a single incoming edge. That's the most common
+ degenerate PHI we'll see here. Finally we ignore PHIs
+ that are associated with the value we're tracking as
+ that object likely dies. */
+ if (EDGE_COUNT (bb->succs) > 1 && EDGE_COUNT (bb->preds) > 1)
+ {
+ for (gphi_iterator gsip = gsi_start_phis (bb);
+ !gsi_end_p (gsip);
+ gsi_next (&gsip))
+ {
+ gphi *phi = gsip.phi ();
+ tree dst = gimple_phi_result (phi);
+
+ if (SSA_NAME_VAR (dst) != SSA_NAME_VAR (name)
+ && !virtual_operand_p (dst))
+ ++n_insns;
+ }
+ }
+
for (gsi = gsi_after_labels (bb);
!gsi_end_p (gsi);
gsi_next_nondebug (&gsi))
@@ -324,6 +355,11 @@ fsm_find_control_statement_thread_paths (tree name,
threaded_through_latch = true;
}
+ /* We are going to remove the control statement at the end of the
+ last block in the threading path. So don't count it against our
+ statement count. */
+ n_insns--;
+
gimple *stmt = get_gimple_control_stmt ((*path)[0]);
gcc_assert (stmt);
/* We have found a constant value for ARG. For GIMPLE_SWITCH
@@ -352,24 +388,6 @@ fsm_find_control_statement_thread_paths (tree name,
== DOMST_NONDOMINATING))
creates_irreducible_loop = true;
- /* PHIs in the final target and only the final target will need
- to be duplicated. So only count those against the number
- of statements. */
- gphi_iterator gsip;
- for (gsip = gsi_start_phis (taken_edge->dest);
- !gsi_end_p (gsip);
- gsi_next (&gsip))
- {
- gphi *phi = gsip.phi ();
- tree dst = gimple_phi_result (phi);
-
- /* We consider any non-virtual PHI as a statement since it
- count result in a constant assignment or copy
- operation. */
- if (!virtual_operand_p (dst))
- ++n_insns;
- }
-
if (path_crosses_loops)
{
if (dump_file && (dump_flags & TDF_DETAILS))
