Revert "[llvm][clang] Allocate a new stack instead of spawning a new … (#135865)

…thread to get more stack space (#133173)"

This change breaks the Clang build on Mac AArch64.

This reverts commit d0c973a. This
reverts commit 429a84f. This reverts
commit 4f64c80.

Author: mysterymath

clang/docs/ReleaseNotes.rst

@@ -195,10 +195,6 @@ Non-comprehensive list of changes in this release
 - Added `__builtin_elementwise_exp10`.
 - For AMDPGU targets, added `__builtin_v_cvt_off_f32_i4` that maps to the `v_cvt_off_f32_i4` instruction.
 - Added `__builtin_elementwise_minnum` and `__builtin_elementwise_maxnum`.
-- Clang itself now uses split stacks instead of threads for allocating more
-  stack space when running on Apple AArch64 based platforms. This means that
-  stack traces of Clang from debuggers, crashes, and profilers may look
-  different than before.
 
 New Compiler Flags
 ------------------

clang/include/clang/Basic/Stack.h

@@ -27,10 +27,7 @@ namespace clang {
 
   /// Call this once on each thread, as soon after starting the thread as
   /// feasible, to note the approximate address of the bottom of the stack.
-  ///
-  /// \param ForceSet set to true if you know the call is near the bottom of a
-  ///                 new stack. Used for split stacks.
-  void noteBottomOfStack(bool ForceSet = false);
+  void noteBottomOfStack();
 
   /// Determine whether the stack is nearly exhausted.
   bool isStackNearlyExhausted();

clang/lib/Basic/Stack.cpp

@@ -13,13 +13,33 @@
 
 #include "clang/Basic/Stack.h"
 #include "llvm/Support/CrashRecoveryContext.h"
-#include "llvm/Support/ProgramStack.h"
 
-static LLVM_THREAD_LOCAL uintptr_t BottomOfStack = 0;
+#ifdef _MSC_VER
+#include <intrin.h>  // for _AddressOfReturnAddress
+#endif
 
-void clang::noteBottomOfStack(bool ForceSet) {
-  if (!BottomOfStack || ForceSet)
-    BottomOfStack = llvm::getStackPointer();
+static LLVM_THREAD_LOCAL void *BottomOfStack = nullptr;
+
+static void *getStackPointer() {
+#if __GNUC__ || __has_builtin(__builtin_frame_address)
+  return __builtin_frame_address(0);
+#elif defined(_MSC_VER)
+  return _AddressOfReturnAddress();
+#else
+  char CharOnStack = 0;
+  // The volatile store here is intended to escape the local variable, to
+  // prevent the compiler from optimizing CharOnStack into anything other
+  // than a char on the stack.
+  //
+  // Tested on: MSVC 2015 - 2019, GCC 4.9 - 9, Clang 3.2 - 9, ICC 13 - 19.
+  char *volatile Ptr = &CharOnStack;
+  return Ptr;
+#endif
+}
+
+void clang::noteBottomOfStack() {
+  if (!BottomOfStack)
+    BottomOfStack = getStackPointer();
 }
 
 bool clang::isStackNearlyExhausted() {
@@ -31,8 +51,7 @@ bool clang::isStackNearlyExhausted() {
   if (!BottomOfStack)
     return false;
 
-  intptr_t StackDiff =
-      (intptr_t)llvm::getStackPointer() - (intptr_t)BottomOfStack;
+  intptr_t StackDiff = (intptr_t)getStackPointer() - (intptr_t)BottomOfStack;
   size_t StackUsage = (size_t)std::abs(StackDiff);
 
   // If the stack pointer has a surprising value, we do not understand this
@@ -47,12 +66,9 @@ bool clang::isStackNearlyExhausted() {
 void clang::runWithSufficientStackSpaceSlow(llvm::function_ref<void()> Diag,
                                             llvm::function_ref<void()> Fn) {
   llvm::CrashRecoveryContext CRC;
-  // Preserve the BottomOfStack in case RunSafelyOnNewStack uses split stacks.
-  uintptr_t PrevBottom = BottomOfStack;
-  CRC.RunSafelyOnNewStack([&] {
-    noteBottomOfStack(true);
+  CRC.RunSafelyOnThread([&] {
+    noteBottomOfStack();
     Diag();
     Fn();
   }, DesiredStackSize);
-  BottomOfStack = PrevBottom;
 }

clang/lib/Frontend/CompilerInstance.cpp

@@ -1265,7 +1265,7 @@ bool CompilerInstance::compileModule(SourceLocation ImportLoc,
 
   // Execute the action to actually build the module in-place. Use a separate
   // thread so that we get a stack large enough.
-  bool Crashed = !llvm::CrashRecoveryContext().RunSafelyOnNewStack(
+  bool Crashed = !llvm::CrashRecoveryContext().RunSafelyOnThread(
       [&]() {
         GenerateModuleFromModuleMapAction Action;
         Instance.ExecuteAction(Action);

llvm/include/llvm/Support/CrashRecoveryContext.h

@@ -97,9 +97,6 @@ class CrashRecoveryContext {
     return RunSafelyOnThread([&]() { Fn(UserData); }, RequestedStackSize);
   }
 
-  bool RunSafelyOnNewStack(function_ref<void()>,
-                           unsigned RequestedStackSize = 0);
-
   /// Explicitly trigger a crash recovery in the current process, and
   /// return failure from RunSafely(). This function does not return.
   [[noreturn]] void HandleExit(int RetCode);

llvm/include/llvm/Support/ProgramStack.h

@@ -213,7 +213,6 @@ inline thread::id get_id() { return std::this_thread::get_id(); }
 
 #else // !LLVM_ENABLE_THREADS
 
-#include "llvm/Support/ErrorHandling.h"
 #include <utility>
 
 namespace llvm {

llvm/include/llvm/Support/thread.h

@@ -295,7 +295,6 @@ add_llvm_component_library(LLVMSupport
   Path.cpp
   Process.cpp
   Program.cpp
-  ProgramStack.cpp
   RWMutex.cpp
   Signals.cpp
   Threading.cpp

llvm/lib/Support/CMakeLists.txt

@@ -10,7 +10,6 @@
 #include "llvm/Config/llvm-config.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/ExitCodes.h"
-#include "llvm/Support/ProgramStack.h"
 #include "llvm/Support/Signals.h"
 #include "llvm/Support/thread.h"
 #include <cassert>
@@ -524,13 +523,3 @@ bool CrashRecoveryContext::RunSafelyOnThread(function_ref<void()> Fn,
     CRC->setSwitchedThread();
   return Info.Result;
 }
-
-bool CrashRecoveryContext::RunSafelyOnNewStack(function_ref<void()> Fn,
-                                               unsigned RequestedStackSize) {
-#ifdef LLVM_HAS_SPLIT_STACKS
-  return runOnNewStack(RequestedStackSize,
-                       function_ref<bool()>([&]() { return RunSafely(Fn); }));
-#else
-  return RunSafelyOnThread(Fn, RequestedStackSize);
-#endif
-}