compiler: reorder optimization passes.

* share/txr/stdlib/compiler.tl (compiler optimize): Perform
the control flow optimizations of jump threading and dead code
elimination first. Then, do the data-flow-assisted
optimizations on the re-calculated control flow graph.
With this, two more useless insructions are shaved off the
pattern matching Ackermann:

  (defun ack (:match)
    ((0 @n) (+ n 1))
    ((@m 0) (ack (- m 1) 1))
    ((@m @n) (ack (- m 1) (ack m (- n 1)))))

It now compiles down to 16 instructions instead of 18;
and the speedup of (ack 3 7) versus interpreted goes
from 36.0 to 37.3 times.

The reason that the new reduction in the code is possible
is that previously, the code being analyzed was in separate
basic blocks, which are now merged together in the dead code
elimination pass.

* share/txr/stdlib/compiler.tl (compiler optimize): Move
calc-liveness and peephole after elim-dead-code.

1 files changed, 2 insertions, 2 deletions

diff --git a/share/txr/stdlib/compiler.tl b/share/txr/stdlib/compiler.tl
index 59050ff5..6b1c1a17 100644
--- a/share/txr/stdlib/compiler.tl
+++ b/share/txr/stdlib/compiler.tl
@@ -1504,10 +1504,10 @@
 (defmeth compiler optimize (me insns)
   (let* ((lt-dregs (mapcar .oreg me.lt-frags))
          (bb (new (basic-blocks insns lt-dregs))))
-    bb.(calc-liveness)
-    bb.(peephole)
     bb.(thread-jumps)
     bb.(elim-dead-code)
+    bb.(calc-liveness)
+    bb.(peephole)
     bb.(get-insns)))
 
 (defun true-const-p (arg)