[Flang][OpenMP] Fix compilation error when a line with Fixed Source Form Conditional Compilation Sentinels is a continuation line

Author: sihuan

flang/lib/Parser/prescan.cpp

@@ -997,20 +997,27 @@ const char *Prescanner::FixedFormContinuationLine(bool mightNeedSpace) {
   }
   tabInCurrentLine_ = false;
   char col1{*nextLine_};
-  if (InCompilerDirective()) {
-    // Must be a continued compiler directive.
-    if (!IsFixedFormCommentChar(col1)) {
-      return nullptr;
-    }
+  if (InCompilerDirective() ||
+      (features_.IsEnabled(LanguageFeature::OpenMP) &&
+          IsFixedFormCommentChar(col1) && nextLine_[1] == '$')) {
     int j{1};
-    for (; j < 5; ++j) {
-      char ch{directiveSentinel_[j - 1]};
-      if (ch == '\0') {
-        break;
-      }
-      if (ch != ToLowerCaseLetter(nextLine_[j])) {
+    if (InCompilerDirective()) {
+      // Must be a continued compiler directive.
+      if (!IsFixedFormCommentChar(col1)) {
         return nullptr;
       }
+      for (; j < 5; ++j) {
+        char ch{directiveSentinel_[j - 1]};
+        if (ch == '\0') {
+          break;
+        }
+        if (ch != ToLowerCaseLetter(nextLine_[j])) {
+          return nullptr;
+        }
+      }
+    } else {
+      // Fixed Source Form Conditional Compilation Sentinels.
+      j = 2;
     }
     for (; j < 5; ++j) {
       if (nextLine_[j] != ' ') {

flang/test/Parser/continuation-in-conditional-compilation.f

@@ -0,0 +1,16 @@
+! RUN: %flang_fc1 -fopenmp -fopenacc -E %s 2>&1 | FileCheck %s
+      program main
+! CHECK: k01=1+1
+      k01=1+
+!$   &  1
+
+! CHECK: !$omp parallel
+!$omp para
+!$omp+llel
+!$omp end parallel
+
+! CHECK-NOT: comment
+!$omp parallel
+!$acc+comment
+!$omp end parallel
+      end