Support unwinding from inline assembly

I've taken the following steps to add unwinding support from inline assembly:

1) Add a new `unwind` "attribute" (like `sideeffect`) to the asm syntax:

```
invoke void asm sideeffect unwind "call thrower", "~{dirflag},~{fpsr},~{flags}"()
    to label %exit unwind label %uexit
```

2.) Add Bitcode writing/reading support + LLVM-IR parsing.

3.) Emit EHLabels around inline assembly lowering (SelectionDAGBuilder + GlobalISel) when `InlineAsm::canThrow` is enabled.

4.) Tweak InstCombineCalls/InlineFunction pass to not mark inline assembly "calls" as nounwind.

5.) Add clang support by introducing a new clobber: "unwind", which lower to the `canThrow` being enabled.

6.) Don't allow unwinding callbr.

Reviewed By: Amanieu

Differential Revision: https://reviews.llvm.org/D95745

1 files changed, 9 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Utils/InlineFunction.cpp b/llvm/lib/Transforms/Utils/InlineFunction.cpp
index be4c828..49be8bb 100644
--- a/llvm/lib/Transforms/Utils/InlineFunction.cpp
+++ b/llvm/lib/Transforms/Utils/InlineFunction.cpp
@@ -45,6 +45,7 @@
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/InlineAsm.h"
 #include "llvm/IR/InstrTypes.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/Instructions.h"
@@ -545,9 +546,16 @@ static BasicBlock *HandleCallsInBlockInlinedThroughInvoke(
     // instructions require no special handling.
     CallInst *CI = dyn_cast<CallInst>(I);
 
-    if (!CI || CI->doesNotThrow() || CI->isInlineAsm())
+    if (!CI || CI->doesNotThrow())
       continue;
 
+    if (CI->isInlineAsm()) {
+      InlineAsm *IA = cast<InlineAsm>(CI->getCalledOperand());
+      if (!IA->canThrow()) {
+        continue;
+      }
+    }
+
     // We do not need to (and in fact, cannot) convert possibly throwing calls
     // to @llvm.experimental_deoptimize (resp. @llvm.experimental.guard) into
     // invokes.  The caller's "segment" of the deoptimization continuation