On 02/04/15 14:20, Sebastian Pop wrote:
Hi,
The attached patch stops the recursion in the detection of FSM jump-threads at
loop phi nodes after having visited a loop phi node. This avoids jump-threading
two iterations forward that were possible due to a flip-flop operation that
exchange the value of the switch control variable as illustrated in the
testcase:
do {
c = read_from_memory;
switch (a) {
case 0:
if (c == ' ')
[...]
else
a = b; // flip-flop
break;
case 1:
a = 0;
b = 15; // this will jump-thread to 15
break;
case 15:
[...]
}
} while (...);
The patch has passed bootstrap and regression testing on x86_64-linux.
Ok to commit?
Thanks,
Sebastian
0001-PR-64878-do-not-jump-thread-across-more-than-one-bac.patch
From 59c486720749fc3d5feac2a5364d52eac60ba2d0 Mon Sep 17 00:00:00 2001
From: Sebastian Pop<s....@samsung.com>
Date: Wed, 4 Feb 2015 11:17:54 -0600
Subject: [PATCH] PR 64878: do not jump thread across more than one back-edge
2015-02-04 Sebastian Pop<s....@samsung.com>
Brian Rzycki<b.rzy...@samsung.com>
PR tree-optimization/64878
* tree-ssa-threadedge.c: Include tree-ssa-loop.h.
(fsm_find_control_statement_thread_paths): Add parameter seen_loop_phi.
Stop recursion at loop phi nodes after having visited a loop phi node.
* testsuite/gcc.dg/tree-ssa/ssa-dom-thread-8.c: New.
+ /* PR64878: do not take more than a loop phi node: it may be a
flip-flop
+ operation across two latch edges. */
The comment doesn't make much sense. Shouldn't it be something like "Do
not walk through more than one loop PHI node"?
OK for the trunk with the comment clarified.
jeff
