[WebAssembly] Make assembler check for proper nesting of control flow.

Summary:
It does so using a simple nesting stack, and gives clear errors upon
violation. This is unique to wasm, since most CPUs do not have
any nested constructs.

Had to add an end of file check to the general assembler for this.

Note: if/else/end instructions are not currently supported in our
tablegen defs, so these tests will be enabled in a follow-up.
They already pass the nesting check.

Reviewers: dschuff, aheejin

Subscribers: sbc100, jgravelle-google, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D55797

llvm-svn: 350078

1 files changed, 107 insertions, 5 deletions

diff --git a/llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp b/llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp
index f463aea..62229d3 100644
--- a/llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp
+++ b/llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp
@@ -172,6 +172,18 @@ class WebAssemblyAsmParser final : public MCTargetAsmParser {
     Instructions,
   } CurrentState = FileStart;
 
+  // For ensuring blocks are properly nested.
+  enum NestingType {
+    Function,
+    Block,
+    Loop,
+    Try,
+    If,
+    Else,
+    Undefined,
+  };
+  std::vector<NestingType> NestingStack;
+
   // We track this to see if a .functype following a label is the same,
   // as this is how we recognize the start of a function.
   MCSymbol *LastLabel = nullptr;
@@ -184,10 +196,6 @@ public:
     setAvailableFeatures(ComputeAvailableFeatures(STI.getFeatureBits()));
   }
 
-  void addSignature(std::unique_ptr<wasm::WasmSignature> &&Sig) {
-    Signatures.push_back(std::move(Sig));
-  }
-
 #define GET_ASSEMBLER_HEADER
 #include "WebAssemblyGenAsmMatcher.inc"
 
@@ -197,10 +205,60 @@ public:
     llvm_unreachable("ParseRegister is not implemented.");
   }
 
-  bool error(const StringRef &Msg, const AsmToken &Tok) {
+  bool error(const Twine &Msg, const AsmToken &Tok) {
     return Parser.Error(Tok.getLoc(), Msg + Tok.getString());
   }
 
+  bool error(const Twine &Msg) {
+    return Parser.Error(Lexer.getTok().getLoc(), Msg);
+  }
+
+  void addSignature(std::unique_ptr<wasm::WasmSignature> &&Sig) {
+    Signatures.push_back(std::move(Sig));
+  }
+
+  std::pair<StringRef, StringRef> nestingString(NestingType NT) {
+    switch (NT) {
+    case Function:
+      return {"function", "end_function"};
+    case Block:
+      return {"block", "end_block"};
+    case Loop:
+      return {"loop", "end_loop"};
+    case Try:
+      return {"try", "end_try"};
+    case If:
+      return {"if", "end_if"};
+    case Else:
+      return {"else", "end_if"};
+    default:
+      llvm_unreachable("unknown NestingType");
+    }
+  }
+
+  void push(NestingType NT) { NestingStack.push_back(NT); }
+
+  bool pop(StringRef Ins, NestingType NT1, NestingType NT2 = Undefined) {
+    if (NestingStack.empty())
+      return error(Twine("End of block construct with no start: ") + Ins);
+    auto Top = NestingStack.back();
+    if (Top != NT1 && Top != NT2)
+      return error(Twine("Block construct type mismatch, expected: ") +
+                   nestingString(Top).second + ", instead got: " + Ins);
+    NestingStack.pop_back();
+    return false;
+  }
+
+  bool ensureEmptyNestingStack() {
+    auto err = !NestingStack.empty();
+    while (!NestingStack.empty()) {
+      error(Twine("Unmatched block construct(s) at function end: ") +
+            nestingString(NestingStack.back()).first);
+      NestingStack.pop_back();
+    }
+    return err;
+  }
+
   bool isNext(AsmToken::TokenKind Kind) {
     auto Ok = Lexer.is(Kind);
     if (Ok)
@@ -327,6 +385,45 @@ public:
     // If no '.', there is no type prefix.
     auto BaseName = NamePair.second.empty() ? NamePair.first : NamePair.second;
 
+    // If this instruction is part of a control flow structure, ensure
+    // proper nesting.
+    if (BaseName == "block") {
+      push(Block);
+    } else if (BaseName == "loop") {
+      push(Loop);
+    } else if (BaseName == "try") {
+      push(Try);
+    } else if (BaseName == "if") {
+      push(If);
+    } else if (BaseName == "else") {
+      if (pop(BaseName, If))
+        return true;
+      push(Else);
+    } else if (BaseName == "catch") {
+      if (pop(BaseName, Try))
+        return true;
+      push(Try);
+    } else if (BaseName == "catch_all") {
+      if (pop(BaseName, Try))
+        return true;
+      push(Try);
+    } else if (BaseName == "end_if") {
+      if (pop(BaseName, If, Else))
+        return true;
+    } else if (BaseName == "end_try") {
+      if (pop(BaseName, Try))
+        return true;
+    } else if (BaseName == "end_loop") {
+      if (pop(BaseName, Loop))
+        return true;
+    } else if (BaseName == "end_block") {
+      if (pop(BaseName, Block))
+        return true;
+    } else if (BaseName == "end_function") {
+      if (pop(BaseName, Function) || ensureEmptyNestingStack())
+        return true;
+    }
+
     while (Lexer.isNot(AsmToken::EndOfStatement)) {
       auto &Tok = Lexer.getTok();
       switch (Tok.getKind()) {
@@ -476,7 +573,10 @@ public:
           TOut.getStreamer().getContext().getOrCreateSymbol(SymName));
       if (CurrentState == Label && WasmSym == LastLabel) {
         // This .functype indicates a start of a function.
+        if (ensureEmptyNestingStack())
+          return true;
         CurrentState = FunctionStart;
+        push(Function);
       }
       auto Signature = make_unique<wasm::WasmSignature>();
       if (parseSignature(Signature.get()))
@@ -565,6 +665,8 @@ public:
     }
     llvm_unreachable("Implement any new match types added!");
   }
+
+  void onEndOfFile() override { ensureEmptyNestingStack(); }
 };
 } // end anonymous namespace