On Tue, Mar 1, 2016 at 10:46 PM, Jeff Law <l...@redhat.com> wrote:
>
>
> 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)
I think this doesn't quite work, to make it match the comment you'd have to add
a SSA_NAME_VAR (dst) != NULL_TREE check as otherwise all anonymous
SSA names count as "the same value we're tracking". Shouldn't you simply
compare the SSA names themselves but for the operand corresponding to
the edge we are threading instead of the PHI result?
Richard.
> + && !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))
>
