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, 28 insertions, 1 deletions

diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index 38d7b77..91a65c7 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -2830,7 +2830,7 @@ Error BitcodeReader::parseConstants() {
     }
     // This version adds support for the asm dialect keywords (e.g.,
     // inteldialect).
-    case bitc::CST_CODE_INLINEASM: {
+    case bitc::CST_CODE_INLINEASM_OLD2: {
       if (Record.size() < 2)
         return error("Invalid record");
       std::string AsmStr, ConstrStr;
@@ -2855,6 +2855,33 @@ Error BitcodeReader::parseConstants() {
           InlineAsm::AsmDialect(AsmDialect));
       break;
     }
+    // This version adds support for the unwind keyword.
+    case bitc::CST_CODE_INLINEASM: {
+      if (Record.size() < 2)
+        return error("Invalid record");
+      std::string AsmStr, ConstrStr;
+      bool HasSideEffects = Record[0] & 1;
+      bool IsAlignStack = (Record[0] >> 1) & 1;
+      unsigned AsmDialect = (Record[0] >> 2) & 1;
+      bool CanThrow = (Record[0] >> 3) & 1;
+      unsigned AsmStrSize = Record[1];
+      if (2 + AsmStrSize >= Record.size())
+        return error("Invalid record");
+      unsigned ConstStrSize = Record[2 + AsmStrSize];
+      if (3 + AsmStrSize + ConstStrSize > Record.size())
+        return error("Invalid record");
+
+      for (unsigned i = 0; i != AsmStrSize; ++i)
+        AsmStr += (char)Record[2 + i];
+      for (unsigned i = 0; i != ConstStrSize; ++i)
+        ConstrStr += (char)Record[3 + AsmStrSize + i];
+      UpgradeInlineAsmString(&AsmStr);
+      V = InlineAsm::get(
+          cast<FunctionType>(getPointerElementFlatType(CurFullTy)), AsmStr,
+          ConstrStr, HasSideEffects, IsAlignStack,
+          InlineAsm::AsmDialect(AsmDialect), CanThrow);
+      break;
+    }
     case bitc::CST_CODE_BLOCKADDRESS:{
       if (Record.size() < 3)
         return error("Invalid record");