[PATCH 1/2] Driver: Add new -truncate option

[Peter Damianov <peter0x44@disroot.org>]

This commit adds a new option to the driver that truncates one file after
linking.

Tested likeso:

$ gcc hello.c -c
$ du -h hello.o
4.0K  hello.o
$ gcc hello.o -truncate hello
$ ./a.out
Hello world
$ du -h hello.o
$ 0   hello.o

$ gcc hello.o -truncate
gcc: error: missing filename after '-truncate'

The motivation for adding this is PR110710. It is used by lto-wrapper to
truncate files in a shell-independent manner.

Signed-off-by: Peter Damianov <peter0x44@disroot.org>
---
 gcc/common.opt |  5 +++++
 gcc/gcc.cc     | 13 +++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/gcc/common.opt b/gcc/common.opt
index ad348844775..3ede2fa8552 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -422,6 +422,11 @@ Display target specific command line options (including assembler and linker opt
 -time
 Driver Alias(time)
 
+;; Truncate the file specified after linking.
+;; This option is used by lto-wrapper to reduce the peak disk when linking with
+;; many .LTRANS units.
+Driver Separate Undocumented MissingArgError(missing filename after %qs)
+
 -verbose
 Driver Alias(v)
 
diff --git a/gcc/gcc.cc b/gcc/gcc.cc
index 728332b8153..00017964295 100644
--- a/gcc/gcc.cc
+++ b/gcc/gcc.cc
@@ -2138,6 +2138,10 @@ static int have_E = 0;
 /* Pointer to output file name passed in with -o. */
 static const char *output_file = 0;
 
+/* Pointer to input file name passed in with -truncate.
+   This file should be truncated after linking. */
+static const char *totruncate_file = 0;
+
 /* This is the list of suffixes and codes (%g/%u/%U/%j) and the associated
    temp file.  If the HOST_BIT_BUCKET is used for %j, no entry is made for
    it here.  */
@@ -4607,6 +4611,10 @@ driver_handle_option (struct gcc_options *opts,
       save_switch ("-o", 1, &arg, validated, true);
       return true;
 
+    case OPT_truncate:
+      totruncate_file = arg;
+      break;
+
     case OPT_pie:
 #ifdef ENABLE_DEFAULT_PIE
       /* -pie is turned on by default.  */
@@ -9273,6 +9281,11 @@ driver::maybe_run_linker (const char *argv0) const
 	       option).  */
 	    error ("%s: linker input file not found: %m", outfiles[i]);
 	}
+
+  if (totruncate_file != NULL && linker_was_run && !seen_error ())
+    /* Truncate file specified by -truncate.
+       Used by lto-wrapper to reduce temporary disk-space usage. */
+    truncate(totruncate_file, 0);
 }
 
 /* The end of "main".  */
-- 
2.39.2