[WebAssembly] Add Wasm exception handling prepare pass

Summary:
This adds a pass that transforms a program to be prepared for Wasm
exception handling. This is using Windows EH instructions and based on
the previous Wasm EH proposal.
(https://github.com/WebAssembly/exception-handling/blob/master/proposals/Exceptions.md)

Reviewers: dschuff, majnemer

Subscribers: jfb, mgorny, sbc100, jgravelle-google, JDevlieghere, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D43746

llvm-svn: 333696

llvm/include/llvm/CodeGen/Passes.h

@@ -329,13 +329,17 @@ namespace llvm {
 
   /// createWinEHPass - Prepares personality functions used by MSVC on Windows,
   /// in addition to the Itanium LSDA based personalities.
-  FunctionPass *createWinEHPass();
+  FunctionPass *createWinEHPass(bool DemoteCatchSwitchPHIOnly = false);
 
   /// createSjLjEHPreparePass - This pass adapts exception handling code to use
   /// the GCC-style builtin setjmp/longjmp (sjlj) to handling EH control flow.
   ///
   FunctionPass *createSjLjEHPreparePass();
 
+  /// createWasmEHPass - This pass adapts exception handling code to use
+  /// WebAssembly's exception handling scheme.
+  FunctionPass *createWasmEHPass();
+
   /// LocalStackSlotAllocation - This pass assigns local frame indices to stack
   /// slots relative to one another and allocates base registers to access them
   /// when it is estimated by the target to be out of range of normal frame

llvm/include/llvm/IR/IntrinsicsWebAssembly.td

@@ -42,7 +42,21 @@ def int_wasm_rethrow : Intrinsic<[], [], [Throws, IntrNoReturn]>;
 
 // Since wasm does not use landingpad instructions, these instructions return
 // exception pointer and selector values until we lower them in WasmEHPrepare.
-def int_wasm_get_exception : Intrinsic<[llvm_ptr_ty], [], [IntrHasSideEffects]>;
-def int_wasm_get_ehselector : Intrinsic<[llvm_i32_ty], [],
+def int_wasm_get_exception : Intrinsic<[llvm_ptr_ty], [llvm_token_ty],
+                                       [IntrHasSideEffects]>;
+def int_wasm_get_ehselector : Intrinsic<[llvm_i32_ty], [llvm_token_ty],
                                         [IntrHasSideEffects]>;
+
+// wasm.catch returns the pointer to the exception object caught by wasm 'catch'
+// instruction.
+def int_wasm_catch : Intrinsic<[llvm_ptr_ty], [llvm_i32_ty],
+                               [IntrHasSideEffects]>;
+
+// WebAssembly EH must maintain the landingpads in the order assigned to them
+// by WasmEHPrepare pass to generate landingpad table in EHStreamer. This is
+// used in order to give them the indices in WasmEHPrepare.
+def int_wasm_landingpad_index: Intrinsic<[], [llvm_i32_ty], [IntrNoMem]>;
+
+// Returns LSDA address of the current function.
+def int_wasm_lsda : Intrinsic<[llvm_ptr_ty], [], [IntrNoMem]>;
 }

llvm/include/llvm/InitializePasses.h

@@ -389,6 +389,7 @@ void initializeUnreachableMachineBlockElimPass(PassRegistry&);
 void initializeVerifierLegacyPassPass(PassRegistry&);
 void initializeVirtRegMapPass(PassRegistry&);
 void initializeVirtRegRewriterPass(PassRegistry&);
+void initializeWasmEHPreparePass(PassRegistry&);
 void initializeWholeProgramDevirtPass(PassRegistry&);
 void initializeWinEHPreparePass(PassRegistry&);
 void initializeWriteBitcodePassPass(PassRegistry&);

llvm/lib/CodeGen/CMakeLists.txt

@@ -158,6 +158,7 @@ add_llvm_library(LLVMCodeGen
   UnreachableBlockElim.cpp
   ValueTypes.cpp
   VirtRegMap.cpp
+  WasmEHPrepare.cpp
   WinEHPrepare.cpp
   XRayInstrumentation.cpp
 

llvm/lib/CodeGen/CodeGen.cpp

@@ -102,6 +102,7 @@ void llvm::initializeCodeGen(PassRegistry &Registry) {
   initializeUnreachableMachineBlockElimPass(Registry);
   initializeVirtRegMapPass(Registry);
   initializeVirtRegRewriterPass(Registry);
+  initializeWasmEHPreparePass(Registry);
   initializeWinEHPreparePass(Registry);
   initializeXRayInstrumentationPass(Registry);
   initializeMIRCanonicalizerPass(Registry);

llvm/lib/CodeGen/TargetPassConfig.cpp

@@ -656,7 +656,12 @@ void TargetPassConfig::addPassesToHandleExceptions() {
     addPass(createDwarfEHPass());
     break;
   case ExceptionHandling::Wasm:
-    // TODO to prevent warning
+    // Wasm EH uses Windows EH instructions, but it does not need to demote PHIs
+    // on catchpads and cleanuppads because it does not outline them into
+    // funclets. Catchswitch blocks are not lowered in SelectionDAG, so we
+    // should remove PHIs there.
+    addPass(createWinEHPass(/*DemoteCatchSwitchPHIOnly=*/false));
+    addPass(createWasmEHPass());
     break;
   case ExceptionHandling::None:
     addPass(createLowerInvokePass());