[LLVM][TableGen] Fix Windows failure in DecoderEmitter

[jurahul]

• Avoid dereferencing the end() iterator to get the end pointer, instead calculate it explicitly
• Fixes a regression introduced in [NFC][LLVM][TableGen] Use decodeULEB128 for OPC_SoftFail emission #136220.
• The windows build failure shows the following call stack:

 | Exception Code: 0x80000003
 |  #0 0x00007ff74bc05897 std::_Vector_const_iterator<class std::_Vector_val<struct std::_Simple_types<unsigned char>>>::operator*(void) const C:\Program Files\Microsoft Visual Studio\2022\Professional\VC\Tools\MSVC\14.37.32822\include\vector:52:0
 |  #1 0x00007ff74bbd3d64 `anonymous namespace'::DecoderEmitter::emitTable D:\buildbot\llvm-worker\clang-cmake-x86_64-avx512-win\llvm\llvm\utils\TableGen\DecoderEmitter.cpp:852:0

[llvmbot]

@llvm/pr-subscribers-tablegen

Author: Rahul Joshi (jurahul)

Changes

• Avoid dereferencing the end() iterator to get the end pointer, instead calculate it explicity.
• This fixes windows build failure seen with the following call stack:

 | Exception Code: 0x80000003
 |  #<!-- -->0 0x00007ff74bc05897 std::_Vector_const_iterator&lt;class std::_Vector_val&lt;struct std::_Simple_types&lt;unsigned char&gt;&gt;&gt;::operator*(void) const C:\Program Files\Microsoft Visual Studio\2022\Professional\VC\Tools\MSVC\14.37.32822\include\vector:52:0
 |  #<!-- -->1 0x00007ff74bbd3d64 `anonymous namespace'::DecoderEmitter::emitTable D:\buildbot\llvm-worker\clang-cmake-x86_64-avx512-win\llvm\llvm\utils\TableGen\DecoderEmitter.cpp:852:0

---

Full diff: https://github.com/llvm/llvm-project/pull/136310.diff

1 Files Affected:

• (modified) llvm/utils/TableGen/DecoderEmitter.cpp (+5-4)

diff --git a/llvm/utils/TableGen/DecoderEmitter.cpp b/llvm/utils/TableGen/DecoderEmitter.cpp
index a3fe49ef25de7..485647d4e5910 100644
--- a/llvm/utils/TableGen/DecoderEmitter.cpp
+++ b/llvm/utils/TableGen/DecoderEmitter.cpp
@@ -833,6 +833,7 @@ void DecoderEmitter::emitTable(formatted_raw_ostream &OS, DecoderTable &Table,
   // appropriate indentation levels.
   DecoderTable::const_iterator I = Table.begin();
   DecoderTable::const_iterator E = Table.end();
+  const uint8_t *const EndPtr = Table.data() + Table.size();
   while (I != E) {
     assert(I < E && "incomplete decode table entry!");
 
@@ -849,7 +850,7 @@ void DecoderEmitter::emitTable(formatted_raw_ostream &OS, DecoderTable &Table,
 
       // ULEB128 encoded start value.
       const char *ErrMsg = nullptr;
-      unsigned Start = decodeULEB128(&*I, nullptr, &*E, &ErrMsg);
+      unsigned Start = decodeULEB128(&*I, nullptr, EndPtr, &ErrMsg);
       assert(ErrMsg == nullptr && "ULEB128 value too large!");
       emitULEB128(I, OS);
 
@@ -903,7 +904,7 @@ void DecoderEmitter::emitTable(formatted_raw_ostream &OS, DecoderTable &Table,
       ++I;
       // Decode the Opcode value.
       const char *ErrMsg = nullptr;
-      unsigned Opc = decodeULEB128(&*I, nullptr, &*E, &ErrMsg);
+      unsigned Opc = decodeULEB128(&*I, nullptr, EndPtr, &ErrMsg);
       assert(ErrMsg == nullptr && "ULEB128 value too large!");
 
       OS << Indent << "MCD::OPC_" << (IsTry ? "Try" : "") << "Decode, ";
@@ -935,12 +936,12 @@ void DecoderEmitter::emitTable(formatted_raw_ostream &OS, DecoderTable &Table,
       OS << Indent << "MCD::OPC_SoftFail, ";
       // Decode the positive mask.
       const char *ErrMsg = nullptr;
-      uint64_t PositiveMask = decodeULEB128(&*I, nullptr, &*E, &ErrMsg);
+      uint64_t PositiveMask = decodeULEB128(&*I, nullptr, EndPtr, &ErrMsg);
       assert(ErrMsg == nullptr && "ULEB128 value too large!");
       emitULEB128(I, OS);
 
       // Decode the negative mask.
-      uint64_t NegativeMask = decodeULEB128(&*I, nullptr, &*E, &ErrMsg);
+      uint64_t NegativeMask = decodeULEB128(&*I, nullptr, EndPtr, &ErrMsg);
       assert(ErrMsg == nullptr && "ULEB128 value too large!");
       emitULEB128(I, OS);
       OS << "// +ve mask: 0x";

[jurahul]

FYI, it hits this check in VC++ vector implementation:

        _STL_VERIFY(
            _Mycont->_Myfirst <= _Ptr && _Ptr < _Mycont->_Mylast, "can't dereference out of range vector iterator");

[topperc]

LGTM