Remove register stack size override in hermes.cpp

Summary:
We are currently overriding any specified register stack size with a
size that is fairly low. This was added to allow the register stack to
be placed on a thread stack when StackRuntime is enabled, however, it
seems like that functionality was removed some time ago, so this limit
no longer serves a purpose.

Remove it so that sizes set through RuntimeConfig are actually
honoured. Set the default RuntimeConfig value to be roughly what the
old limit was (no need to suddenly increase the stack size if we
haven't had problems yet). Keeping the limit low helps us retain the
ability to place the register stack in StackRuntime again in the future.

Reviewed By: mhorowitz

Differential Revision: D42610775

fbshipit-source-id: 94db4e3eb1d6365749a6db8adfe73a5d298f127c

API/hermes/hermes.cpp

@@ -109,15 +109,6 @@ void hermesFatalErrorHandler(
 
 namespace {
 
-// Max size of the runtime's register stack.
-// The runtime register stack needs to be small enough to be allocated on the
-// native thread stack in Android (1MiB) and on MacOS's thread stack (512 KiB)
-// Calculated by: (thread stack size - size of runtime -
-// 8 memory pages for other stuff in the thread)
-static constexpr unsigned kMaxNumRegisters =
-    (512 * 1024 - sizeof(::hermes::vm::Runtime) - 4096 * 8) /
-    sizeof(::hermes::vm::PinnedHermesValue);
-
 void raw_ostream_append(llvh::raw_ostream &os) {}
 
 template <typename Arg0, typename... Args>
@@ -163,11 +154,7 @@ class HermesRuntimeImpl final : public HermesRuntime,
   HermesRuntimeImpl(const vm::RuntimeConfig &runtimeConfig)
       : hermesValues_(runtimeConfig.getGCConfig().getOccupancyTarget()),
         weakHermesValues_(runtimeConfig.getGCConfig().getOccupancyTarget()),
-        rt_(::hermes::vm::Runtime::create(
-            runtimeConfig.rebuild()
-                .withRegisterStack(nullptr)
-                .withMaxNumRegisters(kMaxNumRegisters)
-                .build())),
+        rt_(::hermes::vm::Runtime::create(runtimeConfig)),
         runtime_(*rt_),
         vmExperimentFlags_(runtimeConfig.getVMExperimentFlags()) {
 #ifdef HERMES_ENABLE_DEBUGGER

public/hermes/Public/RuntimeConfig.h

@@ -35,7 +35,7 @@ class PinnedHermesValue;
   F(constexpr, PinnedHermesValue *, RegisterStack, nullptr)            \
                                                                        \
   /* Register Stack Size */                                            \
-  F(constexpr, unsigned, MaxNumRegisters, 1024 * 1024)                 \
+  F(constexpr, unsigned, MaxNumRegisters, 64 * 1024)                   \
                                                                        \
   /* Whether or not the JIT is enabled */                              \
   F(constexpr, bool, EnableJIT, false)                                 \

tools/hermes/hermes.cpp

@@ -112,6 +112,7 @@ static int executeHBCBytecodeFromCL(
           .withEnableHermesInternal(cl::EnableHermesInternal)
           .withEnableHermesInternalTestMethods(
               cl::EnableHermesInternalTestMethods)
+          .withMaxNumRegisters(1024 * 1024)
           .build();
 
   options.basicBlockProfiling = cl::BasicBlockProfiling;

tools/hvm/hvm.cpp

@@ -126,6 +126,7 @@ int main(int argc, char **argv) {
           .withEnableHermesInternal(cl::EnableHermesInternal)
           .withEnableHermesInternalTestMethods(
               cl::EnableHermesInternalTestMethods)
+          .withMaxNumRegisters(1024 * 1024)
           .build();
 
   options.stabilizeInstructionCount = cl::StableInstructionCount;