Enable PGO-based hot/cold splitting for ARM

Summary: D64642514 made hot/cold splitting on ARM be a win when good basic-block profiles are available, which is the case for translations and prologues using PGO (via Vasm block counters). This diff enables hot/cold splitting for such translations by default for ARM.

Reviewed By: jtwarren

Differential Revision: D64642760

fbshipit-source-id: 1a90ee8d5928f37c5b69b6adb00a445300a82987

hphp/doc/configs.specification

@@ -1556,17 +1556,17 @@ The format can be found in hphp/tools/configs/generate_configs.rs
 - uint32_t Jit.RetranslateAllSeconds, UNKNOWN
 - bool Jit.RerunRetranslateAll = false, UNKNOWN
 - bool Jit.BuildOutliningHashes = false, UNKNOWN
-- bool Jit.PGOLayoutSplitHotCold, UNKNOWN
+- bool Jit.PGOLayoutSplitHotCold = true, UNKNOWN
 - bool Jit.PGOLayoutResplitFrozen = true, UNKNOWN
 - bool Jit.PGOVasmBlockCounters = true, UNKNOWN
 - bool Jit.PGOVasmBlockCountersOptPrologue = true, UNKNOWN
 - uint32_t Jit.PGOVasmBlockCountersMaxOpMismatches = 12, UNKNOWN
 - uint32_t Jit.PGOVasmBlockCountersMinEntryValue, UNKNOWN
 - double Jit.PGOVasmBlockCountersHotWeightMultiplier = 0, UNKNOWN
 - bool Jit.LayoutSeparateZeroWeightBlocks = false, UNKNOWN
-- bool Jit.LayoutPrologueSplitHotCold, UNKNOWN
-- bool Jit.LayoutLiveSplitHotCold = true, UNKNOWN
-- bool Jit.LayoutProfileSplitHotCold = true, UNKNOWN
+- bool Jit.LayoutPrologueSplitHotCold = true, UNKNOWN
+- bool Jit.LayoutLiveSplitHotCold, UNKNOWN
+- bool Jit.LayoutProfileSplitHotCold, UNKNOWN
 - bool Jit.LayoutSplitFrozen = true, UNKNOWN
 - uint64_t Jit.LayoutMinHotThreshold = 0, UNKNOWN
 - uint64_t Jit.LayoutMinColdThreshold = 0, UNKNOWN

hphp/runtime/base/configs/jit-impl.cpp

@@ -72,15 +72,15 @@ uint32_t JitLoader::RetranslateAllSecondsDefault() {
   return Cfg::Server::Mode ? 180 : 0;
 }
 
-bool JitLoader::PGOLayoutSplitHotColdDefault() {
-  return arch() != Arch::ARM;
-}
-
 uint32_t JitLoader::PGOVasmBlockCountersMinEntryValueDefault() {
   return Cfg::Server::Mode ? 200 : 0;
 }
 
-bool JitLoader::LayoutPrologueSplitHotColdDefault() {
+bool JitLoader::LayoutLiveSplitHotColdDefault() {
+  return arch() != Arch::ARM;
+}
+
+bool JitLoader::LayoutProfileSplitHotColdDefault() {
   return arch() != Arch::ARM;
 }