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.
Bootstrapped and regression tested on x86_64-linux-gnu. Installed on
the trunk.
Jeff
commit a53bb29a1dffd329aa6235b88b0c2a830aa5a59e
Author: Jeff Law <l...@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 <l...@redhat.com>
+
+ * tree-ssa-threadbackward.c (fsm_find_control_statement_thread_paths):
+ Allow single block jump threading paths.
+
2015-10-13 Tom de Vries <t...@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 <l...@redhat.com>
+
+ * gcc.dg/tree-ssa/ssa-thread-13.c: New test.
+
2015-10-12 Jeff Law <l...@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))
