[Support] On Windows, ensure abort() can be catched several times in a row with CrashRecoveryContext

Before this patch, the CrashRecoveryContext would only catch the first abort(). Any further calls to abort() inside subsquent CrashRecoveryContexts would not be catched. This is because the Windows CRT removes the abort() handler before calling it.

This is part of https://reviews.llvm.org/D70378

include/llvm/Support/CrashRecoveryContext.h

@@ -44,11 +44,11 @@ class CrashRecoveryContextCleanup;
 /// executed in any case, whether crash occurs or not. These actions may be used
 /// to reclaim resources in the case of crash.
 class CrashRecoveryContext {
-  void *Impl;
+  void *Impl = nullptr;
-  CrashRecoveryContextCleanup *head;
+  CrashRecoveryContextCleanup *head = nullptr;
 
 public:
-  CrashRecoveryContext() : Impl(nullptr), head(nullptr) {}
+  CrashRecoveryContext();
   ~CrashRecoveryContext();
 
   /// Register cleanup handler, which is used when the recovery context is

lib/Support/CrashRecoveryContext.cpp

@@ -95,6 +95,13 @@ static void uninstallExceptionOrSignalHandlers();
 
 CrashRecoveryContextCleanup::~CrashRecoveryContextCleanup() {}
 
+CrashRecoveryContext::CrashRecoveryContext() {
+  // On Windows, if abort() was previously triggered (and caught by a previous
+  // CrashRecoveryContext) the Windows CRT removes our installed signal handler,
+  // so we need to install it again.
+  sys::DisableSystemDialogsOnCrash();
+}
+
 CrashRecoveryContext::~CrashRecoveryContext() {
   // Reclaim registered resources.
   CrashRecoveryContextCleanup *i = head;

unittests/Support/CrashRecoveryTest.cpp

@@ -123,4 +123,11 @@ TEST(CrashRecoveryTest, CallOutputDebugString) {
   EXPECT_TRUE(CrashRecoveryContext().RunSafely(outputString));
 }
 
+TEST(CrashRecoveryTest, Abort) {
+  llvm::CrashRecoveryContext::Enable();
+  auto A = []() { abort(); };
+  EXPECT_FALSE(CrashRecoveryContext().RunSafely(A));
+  // Test a second time to ensure we reinstall the abort signal handler.
+  EXPECT_FALSE(CrashRecoveryContext().RunSafely(A));
+}
 #endif