[TableGen] Use SmallVectors for preprocessor include stack. NFC.

[jayfoad]

This is just a minor cleanup and a small step in the direction of using
LLVM containers in preference to STL containers in lib/TableGen.

[llvmbot]

@llvm/pr-subscribers-tablegen

Author: Jay Foad (jayfoad)

Changes

This is just a minor cleanup and a small step in the direction of using
LLVM containers in preference to STL containers in lib/TableGen.

---

Full diff: https://github.com/llvm/llvm-project/pull/121571.diff

2 Files Affected:

• (modified) llvm/lib/TableGen/TGLexer.cpp (+15-26)
• (modified) llvm/lib/TableGen/TGLexer.h (+2-3)

diff --git a/llvm/lib/TableGen/TGLexer.cpp b/llvm/lib/TableGen/TGLexer.cpp
index eee42511804f5e..e23aec6efba59d 100644
--- a/llvm/lib/TableGen/TGLexer.cpp
+++ b/llvm/lib/TableGen/TGLexer.cpp
@@ -81,8 +81,7 @@ TGLexer::TGLexer(SourceMgr &SM, ArrayRef<std::string> Macros) : SrcMgr(SM) {
   TokStart = nullptr;
 
   // Pretend that we enter the "top-level" include file.
-  PrepIncludeStack.push_back(
-      std::make_unique<std::vector<PreprocessorControlDesc>>());
+  PrepIncludeStack.emplace_back();
 
   // Add all macros defined on the command line to the DefinedMacros set.
   // Check invalid macro names and print fatal error if we find one.
@@ -453,8 +452,7 @@ bool TGLexer::LexInclude() {
   CurBuf = SrcMgr.getMemoryBuffer(CurBuffer)->getBuffer();
   CurPtr = CurBuf.begin();
 
-  PrepIncludeStack.push_back(
-      std::make_unique<std::vector<PreprocessorControlDesc>>());
+  PrepIncludeStack.emplace_back();
   return false;
 }
 
@@ -656,17 +654,13 @@ tgtok::TokKind TGLexer::LexExclaim() {
 bool TGLexer::prepExitInclude(bool IncludeStackMustBeEmpty) {
   // Report an error, if preprocessor control stack for the current
   // file is not empty.
-  if (!PrepIncludeStack.back()->empty()) {
+  if (!PrepIncludeStack.back().empty()) {
     prepReportPreprocessorStackError();
 
     return false;
   }
 
   // Pop the preprocessing controls from the include stack.
-  if (PrepIncludeStack.empty()) {
-    PrintFatalError("preprocessor include stack is empty");
-  }
-
   PrepIncludeStack.pop_back();
 
   if (IncludeStackMustBeEmpty) {
@@ -761,7 +755,7 @@ tgtok::TokKind TGLexer::lexPreprocessor(tgtok::TokKind Kind,
     // Regardless of whether we are processing tokens or not,
     // we put the #ifdef control on stack.
     // Note that MacroIsDefined has been canonicalized against ifdef.
-    PrepIncludeStack.back()->push_back(
+    PrepIncludeStack.back().push_back(
         {tgtok::Ifdef, MacroIsDefined, SMLoc::getFromPointer(TokStart)});
 
     if (!prepSkipDirectiveEnd())
@@ -789,10 +783,10 @@ tgtok::TokKind TGLexer::lexPreprocessor(tgtok::TokKind Kind,
   } else if (Kind == tgtok::Else) {
     // Check if this #else is correct before calling prepSkipDirectiveEnd(),
     // which will move CurPtr away from the beginning of #else.
-    if (PrepIncludeStack.back()->empty())
+    if (PrepIncludeStack.back().empty())
       return ReturnError(TokStart, "#else without #ifdef or #ifndef");
 
-    PreprocessorControlDesc IfdefEntry = PrepIncludeStack.back()->back();
+    PreprocessorControlDesc IfdefEntry = PrepIncludeStack.back().back();
 
     if (IfdefEntry.Kind != tgtok::Ifdef) {
       PrintError(TokStart, "double #else");
@@ -801,9 +795,8 @@ tgtok::TokKind TGLexer::lexPreprocessor(tgtok::TokKind Kind,
 
     // Replace the corresponding #ifdef's control with its negation
     // on the control stack.
-    PrepIncludeStack.back()->pop_back();
-    PrepIncludeStack.back()->push_back(
-        {Kind, !IfdefEntry.IsDefined, SMLoc::getFromPointer(TokStart)});
+    PrepIncludeStack.back().back() = {Kind, !IfdefEntry.IsDefined,
+                                      SMLoc::getFromPointer(TokStart)};
 
     if (!prepSkipDirectiveEnd())
       return ReturnError(CurPtr, "only comments are supported after #else");
@@ -822,10 +815,10 @@ tgtok::TokKind TGLexer::lexPreprocessor(tgtok::TokKind Kind,
   } else if (Kind == tgtok::Endif) {
     // Check if this #endif is correct before calling prepSkipDirectiveEnd(),
     // which will move CurPtr away from the beginning of #endif.
-    if (PrepIncludeStack.back()->empty())
+    if (PrepIncludeStack.back().empty())
       return ReturnError(TokStart, "#endif without #ifdef");
 
-    auto &IfdefOrElseEntry = PrepIncludeStack.back()->back();
+    auto &IfdefOrElseEntry = PrepIncludeStack.back().back();
 
     if (IfdefOrElseEntry.Kind != tgtok::Ifdef &&
         IfdefOrElseEntry.Kind != tgtok::Else) {
@@ -836,7 +829,7 @@ tgtok::TokKind TGLexer::lexPreprocessor(tgtok::TokKind Kind,
     if (!prepSkipDirectiveEnd())
       return ReturnError(CurPtr, "only comments are supported after #endif");
 
-    PrepIncludeStack.back()->pop_back();
+    PrepIncludeStack.back().pop_back();
 
     // If we were processing tokens before this #endif, then
     // we should continue it.
@@ -1055,20 +1048,16 @@ bool TGLexer::prepSkipDirectiveEnd() {
 }
 
 bool TGLexer::prepIsProcessingEnabled() {
-  for (const PreprocessorControlDesc &I :
-       llvm::reverse(*PrepIncludeStack.back()))
-    if (!I.IsDefined)
-      return false;
-
-  return true;
+  return all_of(PrepIncludeStack.back(),
+                [](const PreprocessorControlDesc &I) { return I.IsDefined; });
 }
 
 void TGLexer::prepReportPreprocessorStackError() {
-  if (PrepIncludeStack.back()->empty())
+  if (PrepIncludeStack.back().empty())
     PrintFatalError("prepReportPreprocessorStackError() called with "
                     "empty control stack");
 
-  auto &PrepControl = PrepIncludeStack.back()->back();
+  auto &PrepControl = PrepIncludeStack.back().back();
   PrintError(CurBuf.end(), "reached EOF without matching #endif");
   PrintError(PrepControl.SrcPos, "the latest preprocessor control is here");
 
diff --git a/llvm/lib/TableGen/TGLexer.h b/llvm/lib/TableGen/TGLexer.h
index 963d75e52cc8fd..f8b32dc5377f58 100644
--- a/llvm/lib/TableGen/TGLexer.h
+++ b/llvm/lib/TableGen/TGLexer.h
@@ -13,6 +13,7 @@
 #ifndef LLVM_LIB_TABLEGEN_TGLEXER_H
 #define LLVM_LIB_TABLEGEN_TGLEXER_H
 
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSet.h"
 #include "llvm/Support/DataTypes.h"
@@ -21,7 +22,6 @@
 #include <memory>
 #include <set>
 #include <string>
-#include <vector>
 
 namespace llvm {
 template <typename T> class ArrayRef;
@@ -323,8 +323,7 @@ class TGLexer {
   // preprocessing control stacks for the current file and all its
   // parent files.  The back() element is the preprocessing control
   // stack for the current file.
-  std::vector<std::unique_ptr<std::vector<PreprocessorControlDesc>>>
-      PrepIncludeStack;
+  SmallVector<SmallVector<PreprocessorControlDesc>> PrepIncludeStack;
 
   // Validate that the current preprocessing control stack is empty,
   // since we are about to exit a file, and pop the include stack.

[mshockwave]

I have no idea why it was using llvm::reverse here. Maybe the last element usually has a higher chance to bail out?

[jayfoad]

I did think about that, but really if you have nested #ifs I don't see any reason why the inner (or outer) condition would have a higher chance of being false.

[mshockwave]

LGTM