Reland "[WebAssembly] LSDA info generation"

Summary:
This adds support for LSDA (exception table) generation for wasm EH.
Wasm EH mostly follows the structure of Itanium-style exception tables,
with one exception: a call site table entry in wasm EH corresponds to
not a call site but a landing pad.

In wasm EH, the VM is responsible for stack unwinding. After an
exception occurs and the stack is unwound, the control flow is
transferred to wasm 'catch' instruction by the VM, after which the
personality function is called from the compiler-generated code. (Refer
to WasmEHPrepare pass for more information on this part.)

This patch:
- Changes wasm.landingpad.index intrinsic to take a token argument, to
make this 1:1 match with a catchpad instruction
- Stores landingpad index info and catch type info MachineFunction in
before instruction selection
- Lowers wasm.lsda intrinsic to an MCSymbol pointing to the start of an
exception table
- Adds WasmException class with overridden methods for table generation
- Adds support for LSDA section in Wasm object writer

Reviewers: dschuff, sbc100, rnk

Subscribers: mgorny, jgravelle-google, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D52748

llvm-svn: 345345

1 files changed, 42 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/WasmException.h b/llvm/lib/CodeGen/AsmPrinter/WasmException.h
new file mode 100644
index 00000000000..09a9a25ce8d
--- /dev/null
+++ b/llvm/lib/CodeGen/AsmPrinter/WasmException.h
@@ -0,0 +1,42 @@
+//===-- WasmException.h - Wasm Exception Framework -------------*- C++ -*--===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains support for writing WebAssembly exception info into asm
+// files.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIB_CODEGEN_ASMPRINTER_WASMEXCEPTION_H
+#define LLVM_LIB_CODEGEN_ASMPRINTER_WASMEXCEPTION_H
+
+#include "EHStreamer.h"
+#include "llvm/CodeGen/AsmPrinter.h"
+
+namespace llvm {
+
+class LLVM_LIBRARY_VISIBILITY WasmException : public EHStreamer {
+public:
+  WasmException(AsmPrinter *A) : EHStreamer(A) {}
+
+  void endModule() override {}
+  void beginFunction(const MachineFunction *MF) override {}
+  virtual void markFunctionEnd() override;
+  void endFunction(const MachineFunction *MF) override;
+
+protected:
+  // Compute the call site table for wasm EH.
+  void computeCallSiteTable(
+      SmallVectorImpl<CallSiteEntry> &CallSites,
+      const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
+      const SmallVectorImpl<unsigned> &FirstActions) override;
+};
+
+} // End of namespace llvm
+
+#endif