[gcc r13-4203] libcpp/remap: Only override if string matched

[gcc r13-4203] libcpp/remap: Only override if string matched

[Torbjorn Svensson]

https://gcc.gnu.org/g:711f56ad9093b18197ca82415317f4a3748d45ae

commit r13-4203-g711f56ad9093b18197ca82415317f4a3748d45ae
Author: Torbjörn SVENSSON <torbjorn.svensson@foss.st.com>
Date:   Thu Oct 20 22:38:57 2022 +0200

    libcpp/remap: Only override if string matched
    
    For systems with HAVE_DOS_BASED_FILE_SYSTEM set, only override the
    pointer if the backslash pattern matches.
    
    Output without this patch:
    .../gcc/testsuite/gcc.dg/cpp/pr71681-2.c:5:10: fatal error: a/t2.h: No such file or directory
    
    With patch applied, no output and the test case succeeds.
    
    libcpp/ChangeLog
    
            * files.cc: Ensure pattern matches before use.
    
    Signed-off-by: Torbjörn SVENSSON <torbjorn.svensson@foss.st.com>

Diff:
---
 libcpp/files.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libcpp/files.cc b/libcpp/files.cc
index 24208f7b0f8..a18b1caf48d 100644
--- a/libcpp/files.cc
+++ b/libcpp/files.cc
@@ -1833,7 +1833,7 @@ remap_filename (cpp_reader *pfile, _cpp_file *file)
 #ifdef HAVE_DOS_BASED_FILE_SYSTEM
       {
 	const char *p2 = strchr (fname, '\\');
-	if (!p || (p > p2))
+	if (!p || (p2 && p > p2))
 	  p = p2;
       }
 #endif