Add support to do suspend polling on backward branches in JIT'ed code.

The polling is expensive for now as it is done through three
instructions: ld/ld/branch. As a result, a bunch of bonus stuff has
been worked on to mitigate the extra overhead:

- Cleaned up resource flags for memory disambiguation.
- Rewrote load/store elimination and scheduler routines to hide
  the ld/ld latency for GC flag. Seperate the dependency checking into
  memory disambiguation part and resource conflict part.
- Allowed code motion for Dalvik/constant/non-aliasing loads to be
  hoisted above branches for null/range checks.
- Created extended basic blocks following goto instructions so that
  longer instruction streams can be optimized as a whole.

Without the bonus stuff, the performance dropped about ~5-10% on some
benchmarks because of the lack of headroom to hide the polling latency
in tight loops. With the bonus stuff, the performance delta is between
+/-5% with polling code generated. With the bonus stuff but disabling
polling, the new bonus stuff provides consistent performance
improvements:

CaffeineMark  3.6%
Linpack      11.1%
Scimark       9.7%
Sieve        33.0%
Checkers      6.0%

As a result, GC polling is disabled by default but can be turned on
through the -Xjitsuspendpoll flag for experimental purposes.

Change-Id: Ia81fc85de3e2b70e6cc93bc37c2b845892003cdb

1 files changed, 3 insertions, 0 deletions

diff --git a/vm/Init.c b/vm/Init.c
index 4c731c95c..a1e058cb1 100644
--- a/vm/Init.c
+++ b/vm/Init.c
@@ -136,6 +136,7 @@ static void usage(const char* progName)
     dvmFprintf(stderr, "  -Xjitverbose\n");
     dvmFprintf(stderr, "  -Xjitprofile\n");
     dvmFprintf(stderr, "  -Xjitdisableopt\n");
+    dvmFprintf(stderr, "  -Xjitsuspendpoll\n");
 #endif
     dvmFprintf(stderr, "\n");
     dvmFprintf(stderr, "Configured with:"
@@ -966,6 +967,8 @@ static int processOptions(int argc, const char* const argv[],
           } else {
               gDvmJit.disableOpt = -1;
           }
+        } else if (strncmp(argv[i], "-Xjitsuspendpoll", 16) == 0) {
+          gDvmJit.genSuspendPoll = true;
 #endif
 
         } else if (strncmp(argv[i], "-Xstacktracefile:", 17) == 0) {