[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

6 files changed, 151 insertions, 5 deletions

diff --git a/llvm/include/llvm/MC/MCParser/MCTargetAsmParser.h b/llvm/include/llvm/MC/MCParser/MCTargetAsmParser.h
index bb979422f0a..ccf13a6a4fb 100644
--- a/llvm/include/llvm/MC/MCParser/MCTargetAsmParser.h
+++ b/llvm/include/llvm/MC/MCParser/MCTargetAsmParser.h
@@ -490,6 +490,9 @@ public:
                                               MCContext &Ctx) {
     return nullptr;
   }
+
+  // For any checks or cleanups at the end of parsing.
+  virtual void onEndOfFile() {}
 };
 
 } // end namespace llvm
diff --git a/llvm/lib/MC/MCParser/AsmParser.cpp b/llvm/lib/MC/MCParser/AsmParser.cpp
index 545da359ea5..cf42a6f7075 100644
--- a/llvm/lib/MC/MCParser/AsmParser.cpp
+++ b/llvm/lib/MC/MCParser/AsmParser.cpp
@@ -899,6 +899,9 @@ bool AsmParser::Run(bool NoInitialTextSection, bool NoFinalize) {
       eatToEndOfStatement();
   }
 
+  getTargetParser().onEndOfFile();
+  printPendingErrors();
+
   // All errors should have been emitted.
   assert(!hasPendingError() && "unexpected error from parseStatement");
 
diff --git a/llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp b/llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp
index f463aeaf827..62229d390b3 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
 
diff --git a/llvm/test/MC/WebAssembly/basic-assembly-errors.s b/llvm/test/MC/WebAssembly/basic-assembly-errors.s
new file mode 100644
index 00000000000..06fc4f85e7c
--- /dev/null
+++ b/llvm/test/MC/WebAssembly/basic-assembly-errors.s
@@ -0,0 +1,25 @@
+# RUN: not llvm-mc -triple=wasm32-unknown-unknown -mattr=+simd128,+nontrapping-fptoint,+exception-handling < %s 2>&1 | FileCheck %s
+
+    .text
+    .section    .text.main,"",@
+    .type       test0,@function
+# CHECK: End of block construct with no start: end_try
+    end_try
+test0:
+    .functype   test0 () -> ()
+# CHECK: Block construct type mismatch, expected: end_function, instead got: end_loop
+    end_loop
+    block
+# CHECK: Block construct type mismatch, expected: end_block, instead got: end_if
+    end_if
+    try
+    loop
+# CHECK: Block construct type mismatch, expected: end_loop, instead got: end_function
+# CHECK: error: Unmatched block construct(s) at function end: loop
+# CHECK: error: Unmatched block construct(s) at function end: try
+# CHECK: error: Unmatched block construct(s) at function end: block
+# CHECK: error: Unmatched block construct(s) at function end: function
+    end_function
+.Lfunc_end0:
+    .size       test0, .Lfunc_end0-test0
+
diff --git a/llvm/test/MC/WebAssembly/basic-assembly.s b/llvm/test/MC/WebAssembly/basic-assembly.s
index 6d95db48291..e29e47d80aa 100644
--- a/llvm/test/MC/WebAssembly/basic-assembly.s
+++ b/llvm/test/MC/WebAssembly/basic-assembly.s
@@ -59,6 +59,11 @@ test0:
     end_block            # default jumps here.
     i32.const 3
     end_block            # "switch" exit.
+    #if                  # These are not in tablegen defs yet..
+    #if
+    #end_if
+    #else
+    #end_if
     f32x4.add
     # Test correct parsing of instructions with / and : in them:
     # TODO: enable once instruction has been added.
@@ -129,6 +134,11 @@ test0:
 # CHECK-NEXT:      end_block           # label3:
 # CHECK-NEXT:      i32.const 3
 # CHECK-NEXT:      end_block           # label2:
+# DONT-CHECK-NEXT:      if
+# DONT-CHECK-NEXT:      if
+# DONT-CHECK-NEXT:      end_if
+# DONT-CHECK-NEXT:      else
+# DONT-CHECK-NEXT:      end_if
 # CHECK-NEXT:      f32x4.add
 # CHECK-NEXT:      i32.trunc_s/f32
 # CHECK-NEXT:      try
diff --git a/llvm/test/MC/WebAssembly/simd-encodings.s b/llvm/test/MC/WebAssembly/simd-encodings.s
index abb033ca215..1709d0edbde 100644
--- a/llvm/test/MC/WebAssembly/simd-encodings.s
+++ b/llvm/test/MC/WebAssembly/simd-encodings.s
@@ -1,5 +1,8 @@
 # RUN: llvm-mc -show-encoding -triple=wasm32-unkown-unknown -mattr=+sign-ext,+simd128 < %s | FileCheck %s
 
+main:
+    .functype main () -> ()
+
     # CHECK: v128.load 48:p2align=0 # encoding: [0xfd,0x00,0x00,0x30]
     v128.load 48