[WebAssembly] Support instruction selection for catching exceptions
Summary:
This lowers exception catching-related instructions:
1. Lowers `wasm.catch` intrinsic to `catch` instruction
2. Removes `catchpad` and `cleanuppad` instructions; they are not
necessary after isel phase. (`MachineBasicBlock::isEHFuncletEntry()` or
`MachineBasicBlock::isEHPad()` can be used instead.)
3. Lowers `catchret` and `cleanupret` instructions to pseudo `catchret`
and `cleanupret` instructions in isel, which will be replaced with other
instructions in `WebAssemblyExceptionPrepare` pass.
4. Adds 'WebAssemblyExceptionPrepare` pass, which is for running various
transformation for EH. Currently this pass only replaces `catchret` and
`cleanupret` instructions into appropriate wasm instructions to make
this patch successfully run until the end.
Currently this does not handle lowering of intrinsics related to LSDA
info generation (`wasm.landingpad.index` and `wasm.lsda`), because they
cannot be tested without implementing `EHStreamer`'s wasm-specific
handlers. They are marked as TODO, which is needed to make isel pass.
Also this does not generate `try` and `end_try` markers yet, which will
be handled in later patches.
This patch is based on the first wasm EH proposal.
(https://github.com/WebAssembly/exception-handling/blob/master/proposals/Exceptions.md)
Reviewers: dschuff, majnemer
Subscribers: jfb, sbc100, jgravelle-google, sunfish, llvm-commits
Differential Revision: https://reviews.llvm.org/D44090
llvm-svn: 333705
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyExceptionPrepare.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyExceptionPrepare.cpp
new file mode 100644
index 0000000..837e957
--- /dev/null
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyExceptionPrepare.cpp
@@ -0,0 +1,88 @@
+//=== WebAssemblyExceptionPrepare.cpp - WebAssembly Exception Preparation -===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// \brief Does various transformations for exception handling.
+///
+//===----------------------------------------------------------------------===//
+
+#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
+#include "WebAssembly.h"
+#include "WebAssemblySubtarget.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "wasm-exception-prepare"
+
+namespace {
+class WebAssemblyExceptionPrepare final : public MachineFunctionPass {
+ StringRef getPassName() const override {
+ return "WebAssembly Prepare Exception";
+ }
+
+ bool runOnMachineFunction(MachineFunction &MF) override;
+
+ bool replaceFuncletReturns(MachineFunction &MF);
+
+public:
+ static char ID; // Pass identification, replacement for typeid
+ WebAssemblyExceptionPrepare() : MachineFunctionPass(ID) {}
+};
+} // end anonymous namespace
+
+char WebAssemblyExceptionPrepare::ID = 0;
+INITIALIZE_PASS(WebAssemblyExceptionPrepare, DEBUG_TYPE,
+ "WebAssembly Exception Preparation", false, false)
+
+FunctionPass *llvm::createWebAssemblyExceptionPrepare() {
+ return new WebAssemblyExceptionPrepare();
+}
+
+bool WebAssemblyExceptionPrepare::runOnMachineFunction(MachineFunction &MF) {
+ bool Changed = false;
+ if (!MF.getFunction().hasPersonalityFn())
+ return false;
+ Changed |= replaceFuncletReturns(MF);
+ // TODO More transformations will be added
+ return Changed;
+}
+
+bool WebAssemblyExceptionPrepare::replaceFuncletReturns(MachineFunction &MF) {
+ bool Changed = false;
+ const auto &TII = *MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
+
+ for (auto &MBB : MF) {
+ auto Pos = MBB.getFirstTerminator();
+ if (Pos == MBB.end())
+ continue;
+ MachineInstr *TI = &*Pos;
+
+ switch (TI->getOpcode()) {
+ case WebAssembly::CATCHRET: {
+ // Replace a catchret with a branch
+ MachineBasicBlock *TBB = TI->getOperand(0).getMBB();
+ if (!MBB.isLayoutSuccessor(TBB))
+ BuildMI(MBB, TI, TI->getDebugLoc(), TII.get(WebAssembly::BR))
+ .addMBB(TBB);
+ TI->eraseFromParent();
+ Changed = true;
+ break;
+ }
+ case WebAssembly::CLEANUPRET: {
+ // Replace a cleanupret with a rethrow
+ BuildMI(MBB, TI, TI->getDebugLoc(), TII.get(WebAssembly::RETHROW))
+ .addImm(0);
+ TI->eraseFromParent();
+ Changed = true;
+ break;
+ }
+ }
+ }
+ return Changed;
+}