[gcc r12-8439] d: Fix D lexer sometimes fails to compile code read from stdin

[gcc r12-8439] d: Fix D lexer sometimes fails to compile code read from stdin

[Iain Buclaw]

https://gcc.gnu.org/g:f106ef53024cc464ae446189fbad373caaff058e

commit r12-8439-gf106ef53024cc464ae446189fbad373caaff058e
Author: Iain Buclaw <ibuclaw@gdcproject.org>
Date:   Tue May 31 14:45:02 2022 +0200

    d: Fix D lexer sometimes fails to compile code read from stdin
    
    As of gdc-12, the lexer expects there 4 bytes of zero padding at the end
    of the source buffer to mark the end of input.  Sometimes when reading
    from stdin, the data at the end of input is garbage rather than zeroes.
    Fix that by explicitly calling memset past the end of the buffer.
    
            PR d/105544
    
    gcc/d/ChangeLog:
    
            * d-lang.cc (d_parse_file): Zero padding past the end of the stdin
            buffer so the D lexer has a sentinel to stop parsing at.
    
    (cherry picked from commit a0bc7fd42136f124726985b1ab4dcde739cd260e)

Diff:
---
 gcc/d/d-lang.cc | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/gcc/d/d-lang.cc b/gcc/d/d-lang.cc
index dc8560f799a..f078f24fc5e 100644
--- a/gcc/d/d-lang.cc
+++ b/gcc/d/d-lang.cc
@@ -1082,6 +1082,10 @@ d_parse_file (void)
 				      global.params.doHdrGeneration);
 	  modules.push (m);
 
+	  /* Zero the padding past the end of the buffer so the D lexer has a
+	     sentinel.  The lexer only reads up to 4 bytes at a time.  */
+	  memset (buffer + len, '\0', 16);
+
 	  /* Overwrite the source file for the module, the one created by
 	     Module::create would have a forced a `.d' suffix.  */
 	  m->src.length = len;