[PATCH] D58474: [WebAssembly] Fix WasmEHInfo updating in LateEHPrepare

[Heejin Ahn via Phabricator via llvm-commits]

aheejin created this revision.
aheejin added a reviewer: dschuff.
Herald added subscribers: llvm-commits, sunfish, jgravelle-google, sbc100.
Herald added a project: LLVM.

When adding a 'br_on_exn' instruction, we transform code as follows:

- Before:

ehpad:

  %exnref:except_ref = catch
  %exn:i32 = extract_exception
  ...
  call @foo()  // can throw

- After:

ehpad:

  %exnref:except_ref = catch
  br_on_exn %thenbb, $__cpp_exception, %exnref
  br %elsebb

elsebb:

  rethrow

thenbb:

  %exn:i32 = extract_exception
  ...
  call @foo()  // can throw

So if an ehpad ends with an instruction that can throw, there is a
ThrowUnwindDest mapping of <ehpad, otherbb>, which means if an
instruction in 'ehpad' throws it should go to 'otherbb'. In that case,
we should've updated it to <thenbb, otherbb>. This fixes the bug, and
also adds member functions to erase mappings in WasmEHFuncInfo.

It's hard to add a test for this because target-specific
MachineFunctionInfo is not serialized at the moment.


Repository:
  rL LLVM

https://reviews.llvm.org/D58474

Files:
  include/llvm/CodeGen/WasmEHFuncInfo.h
  lib/Target/WebAssembly/WebAssemblyLateEHPrepare.cpp


Index: lib/Target/WebAssembly/WebAssemblyLateEHPrepare.cpp
===================================================================
--- lib/Target/WebAssembly/WebAssemblyLateEHPrepare.cpp
+++ lib/Target/WebAssembly/WebAssemblyLateEHPrepare.cpp
@@ -289,6 +289,11 @@
         .addReg(ExnRefReg);
     BuildMI(EHPad, DL, TII.get(WebAssembly::BR)).addMBB(ElseMBB);
 
+    if (EHInfo->hasThrowUnwindDest(EHPad)) {
+      EHInfo->setThrowUnwindDest(ThenMBB, EHInfo->getThrowUnwindDest(EHPad));
+      EHInfo->eraseThrowUnwindDest(EHPad);
+    }
+
     // When this is a terminate pad with __clang_call_terminate() call, we don't
     // rethrow it anymore and call __clang_call_terminate() with a nullptr
     // argument, which will call std::terminate().
@@ -325,8 +330,11 @@
 
     } else {
       BuildMI(ElseMBB, DL, TII.get(WebAssembly::RETHROW));
-      if (EHInfo->hasEHPadUnwindDest(EHPad))
-        EHInfo->setThrowUnwindDest(ElseMBB, EHInfo->getEHPadUnwindDest(EHPad));
+      if (EHInfo->hasEHPadUnwindDest(EHPad)) {
+        auto *DestMBB = EHInfo->getEHPadUnwindDest(EHPad);
+        EHInfo->setThrowUnwindDest(ElseMBB, DestMBB);
+        ElseMBB->addSuccessor(DestMBB);
+      }
     }
   }
 
Index: include/llvm/CodeGen/WasmEHFuncInfo.h
===================================================================
--- include/llvm/CodeGen/WasmEHFuncInfo.h
+++ include/llvm/CodeGen/WasmEHFuncInfo.h
@@ -52,6 +52,12 @@
   bool hasThrowUnwindDest(const BasicBlock *BB) const {
     return ThrowUnwindMap.count(BB);
   }
+  void eraseEHPadUnwindDest(const BasicBlock *BB) {
+    EHPadUnwindMap.erase(BB);
+  }
+  void eraseThrowUnwindDest(const BasicBlock *BB) {
+    ThrowUnwindMap.erase(BB);
+  }
 
   MachineBasicBlock *getEHPadUnwindDest(MachineBasicBlock *MBB) const {
     return EHPadUnwindMap.lookup(MBB).get<MachineBasicBlock *>();
@@ -71,6 +77,12 @@
   bool hasThrowUnwindDest(MachineBasicBlock *MBB) const {
     return ThrowUnwindMap.count(MBB);
   }
+  void eraseEHPadUnwindDest(MachineBasicBlock *MBB) {
+    EHPadUnwindMap.erase(MBB);
+  }
+  void eraseThrowUnwindDest(MachineBasicBlock *MBB) {
+    ThrowUnwindMap.erase(MBB);
+  }
 };
 
 // Analyze the IR in the given function to build WasmEHFuncInfo.


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