Re: [PATCH] Allow FSM to thread single block cases too

[Richard Biener <richard.guenther@gmail.com>]

On Tue, Oct 13, 2015 at 2:21 PM, Jeff Law <law@redhat.com> wrote:
>
> One of the cases that was missing in the FSM support is threading when the
> path is a single block.  ie, a control statement's output can be statically
> determined just by looking at PHIs in the control statement's block for one
> or incoming edges.
>
> This is necessary to fix a regression if I turn off the old jump threader's
> backedge support.  Just as important, Jan has in the past asked about a
> trivial jump threader to be run during early optimizations.  Limiting the
> FSM bits to this case would likely satisfy that need in the future.

I think he asked for trivial forward threads though due to repeated tests.
I hacked FRE to do this (I think), but maybe some trivial cleanup opportunities
are still left here.  Honza?

Richard.

> Bootstrapped and regression tested on x86_64-linux-gnu.  Installed on the
> trunk.
>
> Jeff
>
> commit a53bb29a1dffd329aa6235b88b0c2a830aa5a59e
> Author: Jeff Law <law@redhat.com>
> Date:   Tue Oct 13 06:19:20 2015 -0600
>
>     [PATCH] Allow FSM to thread single block cases too
>
>         * tree-ssa-threadbackward.c
> (fsm_find_control_statement_thread_paths):
>         Allow single block jump threading paths.
>
>         * gcc.dg/tree-ssa/ssa-thread-13.c: New test.
>
> diff --git a/gcc/ChangeLog b/gcc/ChangeLog
> index d71bcd2..caab533 100644
> --- a/gcc/ChangeLog
> +++ b/gcc/ChangeLog
> @@ -1,3 +1,8 @@
> +2015-10-13  Jeff Law  <law@redhat.com>
> +
> +       * tree-ssa-threadbackward.c
> (fsm_find_control_statement_thread_paths):
> +       Allow single block jump threading paths.
> +
>  2015-10-13  Tom de Vries  <tom@codesourcery.com>
>
>         PR tree-optimization/67476
> diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
> index 4a08f0f..acf6df5 100644
> --- a/gcc/testsuite/ChangeLog
> +++ b/gcc/testsuite/ChangeLog
> @@ -1,3 +1,7 @@
> +2015-10-13  Jeff Law  <law@redhat.com>
> +
> +       * gcc.dg/tree-ssa/ssa-thread-13.c: New test.
> +
>  2015-10-12  Jeff Law  <law@redhat.com>
>
>         * gcc.dg/tree-ssa/ssa-thread-12.c: New test.
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-13.c
> b/gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-13.c
> new file mode 100644
> index 0000000..5051d11
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-13.c
> @@ -0,0 +1,70 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-vrp1-details" } */
> +/* { dg-final { scan-tree-dump "FSM" "vrp1" } } */
> +
> +typedef struct rtx_def *rtx;
> +typedef const struct rtx_def *const_rtx;
> +enum rtx_code
> +{
> +  UNKNOWN, VALUE, DEBUG_EXPR, EXPR_LIST, INSN_LIST, SEQUENCE, ADDRESS,
> +    DEBUG_INSN, INSN, JUMP_INSN, CALL_INSN, BARRIER, CODE_LABEL, NOTE,
> +    COND_EXEC, PARALLEL, ASM_INPUT, ASM_OPERANDS, UNSPEC, UNSPEC_VOLATILE,
> +    ADDR_VEC, ADDR_DIFF_VEC, PREFETCH, SET, USE, CLOBBER, CALL, RETURN,
> +    EH_RETURN, TRAP_IF, CONST_INT, CONST_FIXED, CONST_DOUBLE, CONST_VECTOR,
> +    CONST_STRING, CONST, PC, REG, SCRATCH, SUBREG, STRICT_LOW_PART, CONCAT,
> +    CONCATN, MEM, LABEL_REF, SYMBOL_REF, CC0, IF_THEN_ELSE, COMPARE, PLUS,
> +    MINUS, NEG, MULT, SS_MULT, US_MULT, DIV, SS_DIV, US_DIV, MOD, UDIV,
> UMOD,
> +    AND, IOR, XOR, NOT, ASHIFT, ROTATE, ASHIFTRT, LSHIFTRT, ROTATERT, SMIN,
> +    SMAX, UMIN, UMAX, PRE_DEC, PRE_INC, POST_DEC, POST_INC, PRE_MODIFY,
> +    POST_MODIFY, NE, EQ, GE, GT, LE, LT, GEU, GTU, LEU, LTU, UNORDERED,
> +    ORDERED, UNEQ, UNGE, UNGT, UNLE, UNLT, LTGT, SIGN_EXTEND, ZERO_EXTEND,
> +    TRUNCATE, FLOAT_EXTEND, FLOAT_TRUNCATE, FLOAT, FIX, UNSIGNED_FLOAT,
> +    UNSIGNED_FIX, FRACT_CONVERT, UNSIGNED_FRACT_CONVERT, SAT_FRACT,
> +    UNSIGNED_SAT_FRACT, ABS, SQRT, BSWAP, FFS, CLZ, CTZ, POPCOUNT, PARITY,
> +    SIGN_EXTRACT, ZERO_EXTRACT, HIGH, LO_SUM, VEC_MERGE, VEC_SELECT,
> +    VEC_CONCAT, VEC_DUPLICATE, SS_PLUS, US_PLUS, SS_MINUS, SS_NEG, US_NEG,
> +    SS_ABS, SS_ASHIFT, US_ASHIFT, US_MINUS, SS_TRUNCATE, US_TRUNCATE, FMA,
> +    VAR_LOCATION, DEBUG_IMPLICIT_PTR, ENTRY_VALUE, LAST_AND_UNUSED_RTX_CODE
> +};
> +union rtunion_def
> +{
> +  rtx rt_rtx;
> +};
> +typedef union rtunion_def rtunion;
> +struct rtx_def
> +{
> +  __extension__ enum rtx_code code:16;
> +  union u
> +  {
> +    rtunion fld[1];
> +  }
> +  u;
> +};
> +
> +unsigned int rtx_cost (rtx, enum rtx_code, unsigned char);
> +rtx single_set_2 (const_rtx, rtx);
> +
> +unsigned
> +seq_cost (const_rtx seq, unsigned char speed)
> +{
> +  unsigned cost = 0;
> +  rtx set;
> +  for (; seq; seq = (((seq)->u.fld[2]).rt_rtx))
> +    {
> +      set =
> +       (((((enum rtx_code) (seq)->code) == INSN)
> +         || (((enum rtx_code) (seq)->code) == DEBUG_INSN)
> +         || (((enum rtx_code) (seq)->code) == JUMP_INSN)
> +         || (((enum rtx_code) (seq)->code) ==
> +             CALL_INSN)) ? (((enum rtx_code) ((((seq)->u.fld[4]).rt_rtx))->
> +                             code) ==
> +                            SET ? (((seq)->u.fld[4]).
> +                                   rt_rtx) : single_set_2 (seq,
> +                                                           (((seq)->u.
> +                                                             fld[4]).
> +                                                            rt_rtx))) :
> (rtx)
> +        0);
> +      if (set)
> +       cost += rtx_cost (set, SET, speed);
> +    }
> +}
> diff --git a/gcc/tree-ssa-threadbackward.c b/gcc/tree-ssa-threadbackward.c
> index 5be6ee4..9128094 100644
> --- a/gcc/tree-ssa-threadbackward.c
> +++ b/gcc/tree-ssa-threadbackward.c
> @@ -211,10 +211,6 @@ fsm_find_control_statement_thread_paths (tree name,
>         continue;
>
>        int path_length = path->length ();
> -      /* A path with less than 2 basic blocks should not be jump-threaded.
> */
> -      if (path_length < 2)
> -       continue;
> -
>        if (path_length > PARAM_VALUE (PARAM_MAX_FSM_THREAD_LENGTH))
>         {
>           if (dump_file && (dump_flags & TDF_DETAILS))
>