[flang-commits] [flang] [Flang] bug: preprocessor increases backslash to double backslash (PR #191512)

[via flang-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-flang-driver

Author: SunilKuravinakop

<details>
<summary>Changes</summary>

Correcting the preprocessing (-E) output when '\' is used in a string.
Prior to this fix it was being replaced with "\\".

Issue is in [191463](https://github.com/llvm/llvm-project/issues/191463)

---
Full diff: https://github.com/llvm/llvm-project/pull/191512.diff


2 Files Affected:

- (modified) flang/lib/Parser/prescan.cpp (+3-3) 
- (modified) flang/test/Driver/escaped-backslash.f90 (+2-2) 


``````````diff
diff --git a/flang/lib/Parser/prescan.cpp b/flang/lib/Parser/prescan.cpp
index 78537aef1fdfe..c1dd17400012a 100644
--- a/flang/lib/Parser/prescan.cpp
+++ b/flang/lib/Parser/prescan.cpp
@@ -1014,9 +1014,9 @@ void Prescanner::QuotedCharacterLiteral(
     if (*at_ == '\\') {
       if (escapesEnabled) {
         isEscaped = !isEscaped;
-      } else {
-        // The parser always processes escape sequences, so don't confuse it
-        // when escapes are disabled.
+      } else if (!preprocessingOnly_) {
+        // Except when -E is used, the parser always processes escape sequences,
+        // so don't confuse it when escapes are disabled.
         insert('\\');
       }
     } else {
diff --git a/flang/test/Driver/escaped-backslash.f90 b/flang/test/Driver/escaped-backslash.f90
index 90dd1783dd115..75e4ff3beacdc 100644
--- a/flang/test/Driver/escaped-backslash.f90
+++ b/flang/test/Driver/escaped-backslash.f90
@@ -15,8 +15,8 @@
 ! RUN: %flang_fc1 -E -fbackslash %s  2>&1 | FileCheck %s --check-prefix=UNESCAPED
 
 ! ESCAPED:program Backslash
-! ESCAPED-NEXT:New\\nline
-! ESCAPED-NOT:New\nline
+! ESCAPED-NEXT:New\nline
+! ESCAPED-NOT:New\\nline
 
 ! UNESCAPED:program Backslash
 ! UNESCAPED-NEXT:New\nline

``````````

</details>


https://github.com/llvm/llvm-project/pull/191512