On 2 March 2016 at 00:12, Jeff Law <l...@redhat.com> wrote:
>
> This patch clamps the number of statements to copy when not threading across
> a loop backedge in the FSM/backwards threader. This fixes the bulk of the
> regression in 69196. I'm still evaluating whether or not 69196 can be
> closed, but at the least it's a P2 now.
>
> Bootstrapped and regression tested on x86_64-linux-gnu. Also verified the
> size of the testcase in the BZ was drastically reduced. Installing on the
> trunk.
>
> The best idea I've got for further improvements would be to sort the FSM
> threads based on those which are perceived to be the most profitable. That
> would cause certain less profitable jump threads to be abandoned.
>
> It also appears that the threads through the switch statement ought to be
> realized -- my recollection was those were profitable both from a codesize
> and a speed standpoint. It may be the case that the path to realize those
> is just too long after the other jump threads are handled.
>
> But my overall advice would be that if you care about codesize, use -Os
> which will disable most jump threading optimizations. While the specific
> test included in the BZ wasn't improved by jump threading, in general jump
> threading has been shown to be profitable in an of itself with nice
> secondary benefits as well.
>
> Jeff
>
> commit 3d54e848883bc7c510c41b718aabe1771cb16fbf
> Author: law <law@138bc75d-0d04-0410-961f-82ee72b054a4>
> Date: Tue Mar 1 23:12:10 2016 +0000
>
> PR tree-optimization/69196
> * tree-ssa-threadbackward.c
> (fsm_find_control_statement_thread_paths):
> Appropriately clamp the number of statements to copy when the
> thread path does not traverse a loop backedge.
>
> PR tree-optimization/69196
> * gcc.dg/tree-ssa/pr69196.c: New test.
>
Hi,
This new test (the name is pr69196-1.c BTW), fails
for target arm-none-linux-gnueabihf
--with-cpu cortex-a5
FAIL: gcc.dg/tree-ssa/pr69196-1.c scan-tree-dump vrp1 "FSM did not
thread around loop and would copy too many statements
Christophe.
> git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@233870
> 138bc75d-0d04-0410-961f-82ee72b054a4
>
> diff --git a/gcc/ChangeLog b/gcc/ChangeLog
> index 982a7c0..88f0806 100644
> --- a/gcc/ChangeLog
> +++ b/gcc/ChangeLog
> @@ -8,6 +8,11 @@
>
> PR tree-optimization/69196
> * tree-ssa-threadbackward.c
> (fsm_find_control_statement_thread_paths):
> + Appropriately clamp the number of statements to copy when the
> + thread path does not traverse a loop backedge.
> +
> + 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.
> diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
> index bdc4b11..1e6a850 100644
> --- a/gcc/testsuite/ChangeLog
> +++ b/gcc/testsuite/ChangeLog
> @@ -5,6 +5,9 @@
> 2016-03-01 Jeff Law <l...@redhat.com>
>
> PR tree-optimization/69196
> + * gcc.dg/tree-ssa/pr69196.c: New test.
> +
> + 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/testsuite/gcc.dg/tree-ssa/pr69196-1.c
> b/gcc/testsuite/gcc.dg/tree-ssa/pr69196-1.c
> new file mode 100644
> index 0000000..11c7cf5
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr69196-1.c
> @@ -0,0 +1,138 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-vrp1-details" } */
> +
> +/* { dg-final { scan-tree-dump "FSM did not thread around loop and would
> copy too many statements" "vrp1" } } */
> +
> +
> +typedef __builtin_va_list __gnuc_va_list;
> +typedef __gnuc_va_list va_list;
> +extern void rtems_putc(char c);
> +
> +void vprintk(
> + const char *fmt,
> + va_list ap
> +)
> +{
> + for (; *fmt != '\0'; fmt++) {
> + unsigned base = 0;
> + unsigned width = 0;
> + enum {
> + LFLAG_INT,
> + LFLAG_LONG,
> + LFLAG_LONG_LONG
> + } lflag = LFLAG_INT;
> + _Bool minus = 0;
> + _Bool sign = 0;
> + char lead = ' ';
> + char c = *fmt;
> + long long num;
> +
> + if (c != '%') {
> + rtems_putc(c);
> + continue;
> + }
> +
> + ++fmt; c = *fmt;
> +
> + if (c == '0') {
> + lead = '0';
> + ++fmt; c = *fmt;
> + }
> +
> + if (c == '-') {
> + minus = 1;
> + ++fmt; c = *fmt;
> + }
> +
> + while (c >= '0' && c <= '9' ) {
> + width *= 10;
> + width += ((unsigned) c - '0');
> + ++fmt; c = *fmt;
> + }
> +
> + if (c == 'l') {
> + lflag = LFLAG_LONG;
> + ++fmt; c = *fmt;
> +
> + if (c == 'l') {
> + lflag = LFLAG_LONG_LONG;
> + ++fmt; c = *fmt;
> + }
> + }
> +
> + if ( c == 'c' ) {
> +
> + char chr = (char) __builtin_va_arg(ap,int);
> + rtems_putc(chr);
> + continue;
> + }
> +
> + if ( c == 's' ) {
> + unsigned i, len;
> + char *s, *str;
> +
> + str = __builtin_va_arg(ap,char *);
> +
> + if ( str == ((void *)0) ) {
> + str = "";
> + }
> +
> +
> + for ( len=0, s=str ; *s ; len++, s++ )
> + ;
> +
> +
> + if ( !minus )
> + for ( i=len ; i<width ; i++ )
> + rtems_putc(' ');
> +
> +
> + if (width == 0) {
> + width = len;
> + }
> +
> +
> + for ( i=0 ; i<width && *str ; str++ )
> + rtems_putc(*str);
> +
> +
> + if ( minus )
> + for ( i=len ; i<width ; i++ )
> + rtems_putc(' ');
> +
> + continue;
> + }
> +
> +
> + if ( c == 'o' || c == 'O' ) {
> + base = 8; sign = 0;
> + } else if ( c == 'i' || c == 'I' ||
> + c == 'd' || c == 'D' ) {
> + base = 10; sign = 1;
> + } else if ( c == 'u' || c == 'U' ) {
> + base = 10; sign = 0;
> + } else if ( c == 'x' || c == 'X' ) {
> + base = 16; sign = 0;
> + } else if ( c == 'p' ) {
> + base = 16; sign = 0; lflag = LFLAG_LONG;
> + } else {
> + rtems_putc(c);
> + continue;
> + }
> +
> + switch (lflag) {
> + case LFLAG_LONG:
> + num = sign ? (long long) __builtin_va_arg(ap,long)
> + : (long long) __builtin_va_arg(ap,unsigned long);
> + break;
> + case LFLAG_LONG_LONG:
> + num = __builtin_va_arg(ap,long long);
> + break;
> + case LFLAG_INT:
> + default:
> + num = sign ? (long long) __builtin_va_arg(ap,int)
> + : (long long) __builtin_va_arg(ap,unsigned int);
> + break;
> + }
> + }
> +}
> diff --git a/gcc/tree-ssa-threadbackward.c b/gcc/tree-ssa-threadbackward.c
> index 3028504..747296b 100644
> --- a/gcc/tree-ssa-threadbackward.c
> +++ b/gcc/tree-ssa-threadbackward.c
> @@ -429,6 +429,26 @@ fsm_find_control_statement_thread_paths (tree name,
> continue;
> }
>
> +
> + /* If this path does not thread through the loop latch, then we
> are
> + using the FSM threader to find old style jump threads. This
> + is good, except the FSM threader does not re-use an existing
> + threading path to reduce code duplication.
> +
> + So for that case, drastically reduce the number of statements
> + we are allowed to copy. */
> + if (!threaded_through_latch
> + && (n_insns * PARAM_VALUE (PARAM_FSM_SCALE_PATH_STMTS)
> + >= PARAM_VALUE (PARAM_MAX_JUMP_THREAD_DUPLICATION_STMTS)))
> + {
> + if (dump_file && (dump_flags & TDF_DETAILS))
> + fprintf (dump_file,
> + "FSM did not thread around loop and would copy too
> "
> + "many statements.\n");
> + path->pop ();
> + continue;
> + }
> +
> /* When there is a multi-way branch on the path, then threading
> can
> explode the CFG due to duplicating the edges for that multi-way
> branch. So like above, only allow a multi-way branch on the
> path
>
