[flang] Fixes in preprocessing conditional compilation code when preceded by macros

[shivaramaarao]

The compiler directives and conditional compilation codes are getting ignored in the presence of preprocessor macros. The necessary changes are added to identify the compiler directives and to emit proper preprocessor outputs.

Fixes issue #126459

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[llvmbot]

@llvm/pr-subscribers-flang-parser

Author: None (shivaramaarao)

Changes

The compiler directives and conditional compilation codes are getting ignored in the presence of preprocessor macros. The necessary changes are added to identify the compiler directives and to emit proper preprocessor outputs.

Fixes issue #126459

---

Full diff: https://github.com/llvm/llvm-project/pull/129015.diff

5 Files Affected:

• (modified) flang/include/flang/Parser/parsing.h (+3)
• (modified) flang/lib/Parser/parsing.cpp (+9-1)
• (modified) flang/lib/Parser/prescan.cpp (+1-1)
• (modified) flang/lib/Parser/prescan.h (+3)
• (added) flang/test/Preprocessing/bug126459.f90 (+8)

diff --git a/flang/include/flang/Parser/parsing.h b/flang/include/flang/Parser/parsing.h
index 0c774decb16d3..029b5115707b5 100644
--- a/flang/include/flang/Parser/parsing.h
+++ b/flang/include/flang/Parser/parsing.h
@@ -19,6 +19,7 @@
 #include "llvm/Support/raw_ostream.h"
 #include <optional>
 #include <string>
+#include <unordered_set>
 #include <utility>
 #include <vector>
 
@@ -66,6 +67,7 @@ class Parsing {
   void DumpProvenance(llvm::raw_ostream &) const;
   void DumpParsingLog(llvm::raw_ostream &) const;
   void Parse(llvm::raw_ostream &debugOutput);
+  const char *IsCompilerDirectiveSentinel(const char *, std::size_t) const;
   void ClearLog();
 
   void EmitMessage(llvm::raw_ostream &o, const char *at,
@@ -87,6 +89,7 @@ class Parsing {
   std::optional<Program> parseTree_;
   ParsingLog log_;
   Preprocessor preprocessor_{allCooked_.allSources()};
+  std::unordered_set<std::string> compilerDirectiveSentinels_;
 };
 } // namespace Fortran::parser
 #endif // FORTRAN_PARSER_PARSING_H_
diff --git a/flang/lib/Parser/parsing.cpp b/flang/lib/Parser/parsing.cpp
index 8fcac7b3cacb1..d161809bf7401 100644
--- a/flang/lib/Parser/parsing.cpp
+++ b/flang/lib/Parser/parsing.cpp
@@ -106,6 +106,7 @@ const SourceFile *Parsing::Prescan(const std::string &path, Options options) {
   if (options.showColors) {
     allSources.setShowColors(/*showColors=*/true);
   }
+  compilerDirectiveSentinels_ = prescanner.getCompilerDirectiveSentinels();
   return sourceFile;
 }
 
@@ -153,7 +154,8 @@ void Parsing::EmitPreprocessedSource(
         return ch;
       }};
 
-      if (ch == '!' && lineWasBlankBefore) {
+      if (ch == '!' && lineWasBlankBefore &&
+          IsCompilerDirectiveSentinel((const char *)&atChar + 1, 4)) {
         // Other comment markers (C, *, D) in original fixed form source
         // input card column 1 will have been deleted or normalized to !,
         // which signifies a comment (directive) in both source forms.
@@ -258,6 +260,12 @@ void Parsing::Parse(llvm::raw_ostream &out) {
   finalRestingPlace_ = parseState.GetLocation();
 }
 
+const char *Parsing::IsCompilerDirectiveSentinel(
+    const char *sentinel, std::size_t len) const {
+  const auto iter{compilerDirectiveSentinels_.find(std::string(sentinel, len))};
+  return iter == compilerDirectiveSentinels_.end() ? nullptr : iter->c_str();
+}
+
 void Parsing::ClearLog() { log_.clear(); }
 
 } // namespace Fortran::parser
diff --git a/flang/lib/Parser/prescan.cpp b/flang/lib/Parser/prescan.cpp
index c5939a1e0b6c2..b928ed03a2493 100644
--- a/flang/lib/Parser/prescan.cpp
+++ b/flang/lib/Parser/prescan.cpp
@@ -511,7 +511,7 @@ bool Prescanner::MustSkipToEndOfLine() const {
   if (inFixedForm_ && column_ > fixedFormColumnLimit_ && !tabInCurrentLine_) {
     return true; // skip over ignored columns in right margin (73:80)
   } else if (*at_ == '!' && !inCharLiteral_) {
-    return !IsCompilerDirectiveSentinel(at_);
+    return !IsCompilerDirectiveSentinel(at_ + 1);
   } else {
     return false;
   }
diff --git a/flang/lib/Parser/prescan.h b/flang/lib/Parser/prescan.h
index 08041f93b14b6..9099085d079cc 100644
--- a/flang/lib/Parser/prescan.h
+++ b/flang/lib/Parser/prescan.h
@@ -90,6 +90,9 @@ class Prescanner {
   template <typename... A> Message &Say(A &&...a) {
     return messages_.Say(std::forward<A>(a)...);
   }
+  std::unordered_set<std::string> getCompilerDirectiveSentinels() {
+    return compilerDirectiveSentinels_;
+  }
 
 private:
   struct LineClassification {
diff --git a/flang/test/Preprocessing/bug126459.f90 b/flang/test/Preprocessing/bug126459.f90
new file mode 100644
index 0000000000000..95f3e792560e4
--- /dev/null
+++ b/flang/test/Preprocessing/bug126459.f90
@@ -0,0 +1,8 @@
+! RUN: %flang -fopenmp -E %s 2>&1 | FileCheck %s
+!CHECK: !$ NDIR=0
+program main
+integer NDIR
+#define BLANKMACRO
+
+BLANKMACRO !$ NDIR=0
+end program main