Flip the new block-placement pass to be on by default.

This is mostly to test the waters. I'd like to get results from FNT
build bots and other bots running on non-x86 platforms.

This feature has been pretty heavily tested over the last few months by
me, and it fixes several of the execution time regressions caused by the
inlining work by preventing inlining decisions from radically impacting
block layout.

I've seen very large improvements in yacr2 and ackermann benchmarks,
along with the expected noise across all of the benchmark suite whenever
code layout changes. I've analyzed all of the regressions and fixed
them, or found them to be impossible to fix. See my email to llvmdev for
more details.

I'd like for this to be in 3.1 as it complements the inliner changes,
but if any failures are showing up or anyone has concerns, it is just
a flag flip and so can be easily turned off.

I'm switching it on tonight to try and get at least one run through
various folks' performance suites in case SPEC or something else has
serious issues with it. I'll watch bots and revert if anything shows up.

llvm-svn: 154816

1 files changed, 7 insertions, 6 deletions

diff --git a/llvm/lib/CodeGen/Passes.cpp b/llvm/lib/CodeGen/Passes.cpp
index 53d1fcf7377..13d1bbc3102 100644
--- a/llvm/lib/CodeGen/Passes.cpp
+++ b/llvm/lib/CodeGen/Passes.cpp
@@ -37,8 +37,9 @@ static cl::opt<bool> DisableTailDuplicate("disable-tail-duplicate", cl::Hidden,
     cl::desc("Disable tail duplication"));
 static cl::opt<bool> DisableEarlyTailDup("disable-early-taildup", cl::Hidden,
     cl::desc("Disable pre-register allocation tail duplication"));
-static cl::opt<bool> EnableBlockPlacement("enable-block-placement",
-    cl::Hidden, cl::desc("Enable probability-driven block placement"));
+static cl::opt<bool> DisableBlockPlacement("disable-block-placement",
+    cl::Hidden, cl::desc("Disable the probability-driven block placement, and "
+                         "re-enable the old code placement pass"));
 static cl::opt<bool> EnableBlockPlacementStats("enable-block-placement-stats",
     cl::Hidden, cl::desc("Collect probability-driven block placement stats"));
 static cl::opt<bool> DisableCodePlace("disable-code-place", cl::Hidden,
@@ -610,10 +611,10 @@ void TargetPassConfig::addMachineLateOptimization() {
 /// Add standard basic block placement passes.
 void TargetPassConfig::addBlockPlacement() {
   AnalysisID ID = &NoPassID;
-  if (EnableBlockPlacement) {
-    // MachineBlockPlacement is an experimental pass which is disabled by
-    // default currently. Eventually it should subsume CodePlacementOpt, so
-    // when enabled, the other is disabled.
+  if (!DisableBlockPlacement) {
+    // MachineBlockPlacement is a new pass which subsumes the functionality of
+    // CodPlacementOpt. The old code placement pass can be restored by
+    // disabling block placement, but eventually it will be removed.
     ID = addPass(MachineBlockPlacementID);
   } else {
     ID = addPass(CodePlacementOptID);