[flang-commits] [flang] [flang] Line continuation for !@acc and !@cuf conditional lines (PR #164475)

[Peter Klausler via flang-commits]

https://github.com/klausler created https://github.com/llvm/llvm-project/pull/164475

Some Fortran source-level features that work for OpenMP !$ conditional lines, such as free form line continuation, don't work for OpenACC !@acc or CUDA !@cuf conditional lines.  Make them less particular.

Fixes https://github.com/llvm/llvm-project/issues/164470.

>From 55ed3bbb386a47a5977a0ba897407dd8b1059d81 Mon Sep 17 00:00:00 2001
From: Peter Klausler <pklausler at nvidia.com>
Date: Tue, 21 Oct 2025 11:41:25 -0700
Subject: [PATCH] [flang] Line continuation for !@acc and !@cuf conditional
 lines

Some Fortran source-level features that work for OpenMP !$ conditional
lines, such as free form line continuation, don't work for OpenACC
!@acc or CUDA !@cuf conditional lines.  Make them less particular.

Fixes https://github.com/llvm/llvm-project/issues/164470.
---
 flang/lib/Parser/prescan.cpp           | 26 +++++++++-----------------
 flang/lib/Parser/prescan.h             | 12 +++++++++++-
 flang/test/Preprocessing/bug164470.cuf |  6 ++++++
 3 files changed, 26 insertions(+), 18 deletions(-)
 create mode 100644 flang/test/Preprocessing/bug164470.cuf

diff --git a/flang/lib/Parser/prescan.cpp b/flang/lib/Parser/prescan.cpp
index 66e5b2cbd5c7f..df0372bbe554a 100644
--- a/flang/lib/Parser/prescan.cpp
+++ b/flang/lib/Parser/prescan.cpp
@@ -140,17 +140,9 @@ void Prescanner::Statement() {
       CHECK(*at_ == '!');
     }
     std::optional<int> condOffset;
-    if (InOpenMPConditionalLine()) {
+    if (InOpenMPConditionalLine()) { // !$
       condOffset = 2;
-    } else if (directiveSentinel_[0] == '@' && directiveSentinel_[1] == 'c' &&
-        directiveSentinel_[2] == 'u' && directiveSentinel_[3] == 'f' &&
-        directiveSentinel_[4] == '\0') {
-      // CUDA conditional compilation line.
-      condOffset = 5;
-    } else if (directiveSentinel_[0] == '@' && directiveSentinel_[1] == 'a' &&
-        directiveSentinel_[2] == 'c' && directiveSentinel_[3] == 'c' &&
-        directiveSentinel_[4] == '\0') {
-      // OpenACC conditional compilation line.
+    } else if (InOpenACCOrCUDAConditionalLine()) { // !@acc or !@cuf
       condOffset = 5;
     }
     if (condOffset && !preprocessingOnly_) {
@@ -166,7 +158,8 @@ void Prescanner::Statement() {
     } else {
       // Compiler directive.  Emit normalized sentinel, squash following spaces.
       // Conditional compilation lines (!$) take this path in -E mode too
-      // so that -fopenmp only has to appear on the later compilation.
+      // so that -fopenmp only has to appear on the later compilation
+      // (ditto for !@cuf and !@acc).
       EmitChar(tokens, '!');
       ++at_, ++column_;
       for (const char *sp{directiveSentinel_}; *sp != '\0';
@@ -202,7 +195,7 @@ void Prescanner::Statement() {
       }
       tokens.CloseToken();
       SkipSpaces();
-      if (InOpenMPConditionalLine() && inFixedForm_ && !tabInCurrentLine_ &&
+      if (InConditionalLine() && inFixedForm_ && !tabInCurrentLine_ &&
           column_ == 6 && *at_ != '\n') {
         // !$   0   - turn '0' into a space
         // !$   1   - turn '1' into '&'
@@ -347,7 +340,7 @@ void Prescanner::Statement() {
       while (CompilerDirectiveContinuation(tokens, line.sentinel)) {
         newlineProvenance = GetCurrentProvenance();
       }
-      if (preprocessingOnly_ && inFixedForm_ && InOpenMPConditionalLine() &&
+      if (preprocessingOnly_ && inFixedForm_ && InConditionalLine() &&
           nextLine_ < limit_) {
         // In -E mode, when the line after !$ conditional compilation is a
         // regular fixed form continuation line, append a '&' to the line.
@@ -1360,11 +1353,10 @@ const char *Prescanner::FixedFormContinuationLine(bool atNewline) {
               features_.IsEnabled(LanguageFeature::OldDebugLines))) &&
       nextLine_[1] == ' ' && nextLine_[2] == ' ' && nextLine_[3] == ' ' &&
       nextLine_[4] == ' '};
-  if (InCompilerDirective() &&
-      !(InOpenMPConditionalLine() && !preprocessingOnly_)) {
+  if (InCompilerDirective() && !(InConditionalLine() && !preprocessingOnly_)) {
     // !$ under -E is not continued, but deferred to later compilation
     if (IsFixedFormCommentChar(col1) &&
-        !(InOpenMPConditionalLine() && preprocessingOnly_)) {
+        !(InConditionalLine() && preprocessingOnly_)) {
       int j{1};
       for (; j < 5; ++j) {
         char ch{directiveSentinel_[j - 1]};
@@ -1443,7 +1435,7 @@ const char *Prescanner::FreeFormContinuationLine(bool ampersand) {
   }
   p = SkipWhiteSpaceIncludingEmptyMacros(p);
   if (InCompilerDirective()) {
-    if (InOpenMPConditionalLine()) {
+    if (InConditionalLine()) {
       if (preprocessingOnly_) {
         // in -E mode, don't treat !$ as a continuation
         return nullptr;
diff --git a/flang/lib/Parser/prescan.h b/flang/lib/Parser/prescan.h
index fc38adb926530..5e7481781d944 100644
--- a/flang/lib/Parser/prescan.h
+++ b/flang/lib/Parser/prescan.h
@@ -171,7 +171,17 @@ class Prescanner {
   bool InOpenMPConditionalLine() const {
     return directiveSentinel_ && directiveSentinel_[0] == '$' &&
         !directiveSentinel_[1];
-    ;
+  }
+  bool InOpenACCOrCUDAConditionalLine() const {
+    return directiveSentinel_ && directiveSentinel_[0] == '@' &&
+        ((directiveSentinel_[1] == 'a' && directiveSentinel_[2] == 'c' &&
+             directiveSentinel_[3] == 'c') ||
+            (directiveSentinel_[1] == 'c' && directiveSentinel_[2] == 'u' &&
+                directiveSentinel_[3] == 'f')) &&
+        directiveSentinel_[4] == '\0';
+  }
+  bool InConditionalLine() const {
+    return InOpenMPConditionalLine() || InOpenACCOrCUDAConditionalLine();
   }
   bool InFixedFormSource() const {
     return inFixedForm_ && !inPreprocessorDirective_ && !InCompilerDirective();
diff --git a/flang/test/Preprocessing/bug164470.cuf b/flang/test/Preprocessing/bug164470.cuf
new file mode 100644
index 0000000000000..3e959f40d2e3f
--- /dev/null
+++ b/flang/test/Preprocessing/bug164470.cuf
@@ -0,0 +1,6 @@
+!RUN: %flang_fc1 -x cuda -fdebug-unparse %s 2>&1 | FileCheck %s
+!CHECK: ATTRIBUTES(DEVICE) FUNCTION foo()
+!@cuf attributes(device) &
+function foo()
+  foo = 1.
+end