[flang] Fix issue when macro is followed by OpenMP pragma

[shivaramaarao]

When a macro is followed by OpenMP pragma it is considered as comment and ignored. The function IsCompilerDirectiveSentinel expects the compiler directive argument without the prefix comment character. This is fixed in this commit.

Fixes #117693

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[llvmbot]

@llvm/pr-subscribers-flang-parser

Author: None (shivaramaarao)

Changes

When a macro is followed by OpenMP pragma it is considered as comment and ignored. The function IsCompilerDirectiveSentinel expects the compiler directive argument without the prefix comment character. This is fixed in this commit.

Fixes #117693

---

Full diff: https://github.com/llvm/llvm-project/pull/123035.diff

2 Files Affected:

• (modified) flang/lib/Parser/prescan.cpp (+1-1)
• (added) flang/test/Preprocessing/bug117693.f90 (+14)

diff --git a/flang/lib/Parser/prescan.cpp b/flang/lib/Parser/prescan.cpp
index c5939a1e0b6c2c..50a9193d0a57b3 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/test/Preprocessing/bug117693.f90 b/flang/test/Preprocessing/bug117693.f90
new file mode 100644
index 00000000000000..ced7927606e623
--- /dev/null
+++ b/flang/test/Preprocessing/bug117693.f90
@@ -0,0 +1,14 @@
+! RUN: %flang -fopenmp -E %s 2>&1 | FileCheck %s
+!CHECK: !$OMP DO SCHEDULE(STATIC)
+program main
+IMPLICIT NONE
+INTEGER:: I
+#define OMPSUPPORT
+!$ INTEGER :: omp_id
+!$OMP PARALLEL DO
+OMPSUPPORT !$OMP DO SCHEDULE(STATIC)
+DO I=1,100
+print *, omp_id
+ENDDO
+!$OMP END PARALLEL DO
+end program

[github-actions]

⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️

You can test this locally with the following command:

git-clang-format --diff eb96c8c105226956c8ed5ab30699206f53de74f7 bfc3d201256ecbdc77402758dae955048384ef78 --extensions cpp -- flang/lib/Parser/prescan.cpp

View the diff from clang-format here.

diff --git a/flang/lib/Parser/prescan.cpp b/flang/lib/Parser/prescan.cpp
index 50a9193d0a..b928ed03a2 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_+1);
+    return !IsCompilerDirectiveSentinel(at_ + 1);
   } else {
     return false;
   }

[shivaramaarao]

I am seeing a side effect with this change.

program main
INTEGER::n
!$OMP PARALLEL DO SCHEDULE(STATIC) DEFAULT(NONE) !$OMP PRIVATE
DO I=1,100
ENDDO
END PROGRAM

The comment is not getting ignored by the preprocessor.

[shivaramaarao]

I do see more cases to be handled. currently for the source lines that begins with MACRO, characters after "!" are discarded and many issues are hidden.
We need to handle
a) comments after compiler directives
e.g MACRO !$ OMP
b) conditional statements
e.g MACRO !$ ndim=0
c) continuation lines
e.g MACRO !$OMP !comment &
MACRO !$OMP
d) compiler directives that are actually comments
MACRO !$OMP !$OMP

When I was looking into the code, I feel we might need to make design changes to existing implementation that handles macro replacement to consider all these cases. Can someone please comment on this?

[shivaramaarao]

The recent pull request addresses the issue with comments and continuation lines. The conditional compilation issue will be addressed as separate pull request.

[shivaramaarao]

Is the PR ok to submit? If So, I can ask some of our AMD engineers to commit and we will follow up on any regressions.