[Clang] Cover '#pragma clang __debug overflow_stack' in tests

[aganea]

Summary

Previously, #pragma clang __debug overflow_stack wasn't really working, the function was simply looping and not overflowing.
I tested this in various configurations, with Clang 9, MSVC 2017/2019 and GCC 9 on Ubuntu.

[aganea]

clang/lib/Lex/Pragma.cpp

1148

Would it be better if we had something like LLVM_[DISABLE|ENABLE]_OPT in Compiler.h instead of the #ifdefs? That would map to #pragma clang optimize [off|on] (and corresponding #pragma on MSVC/GCC). Note that there's no way I know of to disable optimizations on a per-function basis on MSVC.

[aganea]

Withdrawing this, I found an crash in Debug build. I think this can't work without doing all the crash processing in a separate, pre-allocated thread.

clang/lib/Lex/Pragma.cpp

void HandleCaptured(Preprocessor &PP) {
     Toks[0].startToken();
     Toks[0].setKind(tok::annot_pragma_captured);
     Toks[0].setLocation(NameLoc);
 
     PP.EnterTokenStream(Toks, /*DisableMacroExpansion=*/true,
                         /*IsReinject=*/false);
   }
 
+#ifdef __clang__
+  __attribute__((optnone))
+#elif __GNUC__
+  __attribute__((optimize("O0")))
+#elif _MSC_VER
 // Disable MSVC warning about runtime stack overflow.
-#ifdef _MSC_VER
-    #pragma warning(disable : 4717)
+#pragma optimize("", off)
 #endif
-  static void DebugOverflowStack(void (*P)() = nullptr) {
-    void (*volatile Self)(void(*P)()) = DebugOverflowStack;
-    Self(reinterpret_cast<void(*)()>(Self));
+  static void
+  DebugOverflowStack(void (*P)() = nullptr, unsigned *V = nullptr) {
+    unsigned A[16384]{1};
+    void (*volatile Self)(void (*P)(), unsigned *) = DebugOverflowStack;
+    Self(reinterpret_cast<void (*)()>(Self), A);
   }
-#ifdef _MSC_VER
-    #pragma warning(default : 4717)
+#if !defined(__clang__) && defined(_MSC_VER)
+#pragma optimize("", on)
 #endif
 };
 
 /// PragmaDiagnosticHandler - e.g. '\#pragma GCC diagnostic ignored "-Wformat"'
 struct PragmaDiagnosticHandler : public PragmaHandler {
 private:
   const char *Namespace;
 

clang/test/Driver/crash-report.c

 // RUN: cat %t/crash-report-*.sh | FileCheck --check-prefix=CHECKSH %s
 
 // RUN: env TMPDIR=%t TEMP=%t TMP=%t RC_DEBUG_OPTIONS=1                  \
 // RUN:  CC_PRINT_HEADERS=1 CC_LOG_DIAGNOSTICS=1                         \
 // RUN:  not %clang %s @%t.rsp -DCRASH 2>&1 | FileCheck %s
 // RUN: cat %t/crash-report-*.c | FileCheck --check-prefix=CHECKSRC %s
 // RUN: cat %t/crash-report-*.sh | FileCheck --check-prefix=CHECKSH %s
 
+// RUN: env TMPDIR=%t TEMP=%t TMP=%t RC_DEBUG_OPTIONS=1                  \
+// RUN:  CC_PRINT_HEADERS=1 CC_LOG_DIAGNOSTICS=1                         \
+// RUN:  not %clang %s @%t.rsp -DOVERFLOW 2>&1 | FileCheck %s
+// RUN: cat %t/crash-report-*.c | FileCheck --check-prefix=CHECKSRC %s
+// RUN: cat %t/crash-report-*.sh | FileCheck --check-prefix=CHECKSH %s
+
 // REQUIRES: crash-recovery
 
 #ifdef PARSER
 #pragma clang __debug parser_crash
 #elif CRASH
 #pragma clang __debug crash
+#elif OVERFLOW
+#pragma clang __debug overflow_stack
 #endif
 
 // CHECK: Preprocessed source(s) and associated run script(s) are located at:
 // CHECK-NEXT: note: diagnostic msg: {{.*}}crash-report-{{.*}}.c
 FOO
 // CHECKSRC: FOO
 // CHECKSH: # Crash reproducer
 // CHECKSH-NEXT: # Driver args: {{.*}}"-fsyntax-only"