[clang] Add -fignore-exceptions

Summary:

This is trying to implement the functionality proposed in:
http://lists.llvm.org/pipermail/cfe-dev/2017-April/053417.html
An exception can throw, but no cleanup is going to happen.
A module compiled with exceptions on, can catch the exception throws
from module compiled with -fignore-exceptions.

The use cases for enabling this option are:
1. Performance analysis of EH instrumentation overhead
2. The ability to QA non EH functionality when EH functionality is not available.
3. User of EH enabled headers knows the calls won't throw in their program and
   wants the performance gain from ignoring EH construct.

The implementation tried to accomplish that by removing any landing pad code
 that might get generated.

Reviewed by: aaron.ballman

Differential Revision: https://reviews.llvm.org/D72644

1 files changed, 7 insertions, 5 deletions

diff --git a/clang/lib/CodeGen/CGException.cpp b/clang/lib/CodeGen/CGException.cpp
index fffd989..a542c3d 100644
--- a/clang/lib/CodeGen/CGException.cpp
+++ b/clang/lib/CodeGen/CGException.cpp
@@ -703,12 +703,12 @@ llvm::BasicBlock *CodeGenFunction::getInvokeDestImpl() {
   assert(EHStack.requiresLandingPad());
   assert(!EHStack.empty());
 
-  // If exceptions are disabled and SEH is not in use, then there is no invoke
-  // destination. SEH "works" even if exceptions are off. In practice, this
-  // means that C++ destructors and other EH cleanups don't run, which is
+  // If exceptions are disabled/ignored and SEH is not in use, then there is no
+  // invoke destination. SEH "works" even if exceptions are off. In practice,
+  // this means that C++ destructors and other EH cleanups don't run, which is
   // consistent with MSVC's behavior.
   const LangOptions &LO = CGM.getLangOpts();
-  if (!LO.Exceptions) {
+  if (!LO.Exceptions || LO.IgnoreExceptions) {
     if (!LO.Borland && !LO.MicrosoftExt)
       return nullptr;
     if (!currentFunctionUsesSEHTry())
@@ -751,7 +751,9 @@ llvm::BasicBlock *CodeGenFunction::getInvokeDestImpl() {
 
 llvm::BasicBlock *CodeGenFunction::EmitLandingPad() {
   assert(EHStack.requiresLandingPad());
-
+  assert(!CGM.getLangOpts().IgnoreExceptions &&
+         "LandingPad should not be emitted when -fignore-exceptions are in "
+         "effect.");
   EHScope &innermostEHScope = *EHStack.find(EHStack.getInnermostEHScope());
   switch (innermostEHScope.getKind()) {
   case EHScope::Terminate: