bypass indirection through pointer objects to access stdin/out/err

by ABI, the public stdin/out/err macros use extern pointer objects,
and this is necessary to avoid copy relocations that would be
expensive and make the size of the FILE structure part of the ABI.
however, internally it makes sense to access the underlying FILE
objects directly. this avoids both an indirection through the GOT to
find the address of the stdin/out/err pointer objects (which can't be
computed PC-relative because they may have been moved to the main
program by copy relocations) and an indirection through the resulting
pointer object.

in most places this is just a minor optimization, but in the case of
getchar and putchar (and the unlocked versions thereof), ipa constant
propagation makes all accesses to members of stdin/out PC-relative or
GOT-relative, possibly reducing register pressure as well.

1 files changed, 5 insertions, 3 deletions

diff --git a/src/stdio/stdin.c b/src/stdio/stdin.c
index 171ff22a..5aa5262c 100644
--- a/src/stdio/stdin.c
+++ b/src/stdio/stdin.c
@@ -1,7 +1,9 @@
 #include "stdio_impl.h"
 
+#undef stdin
+
 static unsigned char buf[BUFSIZ+UNGET];
-static FILE f = {
+hidden FILE __stdin_FILE = {
 	.buf = buf+UNGET,
 	.buf_size = sizeof buf-UNGET,
 	.fd = 0,
@@ -11,5 +13,5 @@ static FILE f = {
 	.close = __stdio_close,
 	.lock = -1,
 };
-FILE *const stdin = &f;
-FILE *volatile __stdin_used = &f;
+FILE *const stdin = &__stdin_FILE;
+FILE *volatile __stdin_used = &__stdin_FILE;