[FLANG][OPENMP] Fix handling of continuation lines in mixed OpenMP an… (#120714)

…d Fortran free-form 
OpenMP feature was not enabled in the flang-new for the continuation
line, when we used the continuation line marker in combination of
free-form and OpenMP directive, it was throwing an error. PR is the fix
for that issue.

Added a fix for the following issue
#89559

Author: Karthikdhondi

flang/lib/Parser/prescan.cpp

@@ -1289,14 +1289,18 @@ const char *Prescanner::FreeFormContinuationLine(bool ampersand) {
     return nullptr;
   }
   p = SkipWhiteSpace(p);
-  if (InCompilerDirective()) {
-    if (*p++ != '!') {
-      return nullptr;
-    }
-    for (const char *s{directiveSentinel_}; *s != '\0'; ++p, ++s) {
-      if (*s != ToLowerCaseLetter(*p)) {
-        return nullptr;
+  if (*p == '!') {
+    ++p;
+    if (InCompilerDirective()) {
+      for (const char *s{directiveSentinel_}; *s != '\0'; ++p, ++s) {
+        if (*s != ToLowerCaseLetter(*p)) {
+          return nullptr;
+        }
       }
+    } else if (features_.IsEnabled(LanguageFeature::OpenMP) && *p == '$') {
+      ++p;
+    } else {
+      return nullptr;
     }
     p = SkipWhiteSpace(p);
     if (*p == '&') {

flang/test/Parser/OpenMP/compiler-directive-continuation.f90

@@ -0,0 +1,44 @@
+! RUN: %flang_fc1 -fopenmp -E %s 2>&1 | FileCheck %s --check-prefix=CHECK-OMP
+! RUN: %flang_fc1 -E %s 2>&1 | FileCheck %s 
+
+
+! Test in mixed way, i.e., combination of Fortran free source form 
+! and free source form with conditional compilation sentinel.
+! CHECK-LABEL: subroutine mixed_form1()
+! CHECK-OMP: i = 1 +100+ 1000+ 10 + 1 +1000000000 + 1000000
+! CHECK: i = 1 + 10 + 10000 + 1000000
+subroutine mixed_form1()
+   i = 1 &
+  !$+100&
+  !$&+ 1000&
+   &+ 10 + 1&
+  !$& +100000&
+   &0000 + 1000000
+end subroutine	
+
+
+! Testing continuation lines in only Fortran Free form Source
+! CHECK-LABEL: subroutine mixed_form2()
+! CHECK-OMP: i = 1 +10 +100 + 1000 + 10000
+! CHECK: i = 1 +10 +100 + 1000 + 10000
+subroutine mixed_form2()
+   i = 1 &
+   +10 &
+   &+100
+   & + 1000 &
+   + 10000
+end subroutine
+
+
+! Testing continuation line in only free source form conditional compilation sentinel.
+! CHECK-LABEL: subroutine mixed_form3()
+! CHECK-OMP: i=0
+! CHECK-OMP: i = 1 +10 +100+1000
+subroutine mixed_form3()
+   !$ i=0
+   !$ i = 1 &
+   !$ & +10 &
+   !$&+100&
+   !$ +1000 
+end subroutine
+