tgt-vlog95: Don't strip leading null-bytes from string literals

When a string literal is used in a context where it needs to be wider than
it is it will get left-padded with null-bytes. When the vlog95 backend
emits the string literal it will strip the leading null-bytes as it results
in much more legible code.

Unfortunately there are some corner cases where this results in a change of
behavior of the generated code compared to the original. E.g. if the
context that caused the width expansion has been removed by optimization.
`$display(0 ? "Yes" : "No")` should print " No" due to width expansion, but
when running through the vlog95 backend it will print "No".

Another scenario where there is a change in behavior is when a null byte
was explicitly added at the front of a string literal. E.g. $bits("\000ab")
should print 24, but will print 16 when running through the vlog95 backend.

To mitigate this remove the stripping of the leading null-bytes from the
vlog95 backend. This results in slightly less legible code being generated
in some cases, but makes sure that the code is always correct.

Signed-off-by: Lars-Peter Clausen <[email protected]>

tgt-vlog95/numbers.c

@@ -346,13 +346,9 @@ static void remove_two_chars(char* str)
 void emit_string(const char* string)
 {
       char *buffer = strdup(string);
-      char *bptr = buffer;
       char *cptr;
       fprintf(vlog_out, "\"");
-	/* Prune any leading escaped NULL bytes. */
-      while ((bptr[0] == '\\') && (bptr[1] == '0') &&
-             (bptr[2] == '0') && (bptr[3] == '0')) bptr += 4;
-      for (cptr = bptr; *cptr; cptr += 1) {
+      for (cptr = buffer; *cptr; cptr += 1) {
 	    if (*cptr == '\\') {
 		    /* Replace any \011 with \t */
 		  if ((cptr[1] == '0') && (cptr[2] == '1') &&
@@ -381,7 +377,7 @@ void emit_string(const char* string)
 		  } else cptr += 3;
 	    }
       }
-      if (*bptr) fprintf(vlog_out, "%s", bptr);
+      if (*buffer) fprintf(vlog_out, "%s", buffer);
       free(buffer);
       fprintf(vlog_out, "\"");
 }