http://llvm.org/bugs/show_bug.cgi?id=9520
Summary: Optimizing a data var to a BSS one drops explicit
section attribute
Product: clang
Version: trunk
Platform: PC
OS/Version: Linux
Status: NEW
Severity: normal
Priority: P
Component: LLVM Codegen
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
Hi. Apologies if I have the wrong component -- not sure where exactly this
optimization happens.
Compiling this code:
void trial(int arg)
{
static int __attribute__ ((__section__ (".init.data"))) var = 42;
if (arg)
var = 0;
printf("%i\n", var);
}
clang -O1 cunningly spots that "var" only ever holds one of two values and
replaces it with a 1-byte flag in BSS that it uses to generate the right
value at run time. That's great, except that I explicitly marked the variable
with the section I want it in, and now it's in BSS. A more complex version of
this trips up a compile-time check in Xen that init-only code has all its
variables in init-only data/bss sections.
Can this optimization be made to respect explicit section attributes?
I'm using:
clang version 2.9 (trunk 125745)
Target: x86_64-unknown-linux-gnu
Thread model: posix
Cheers,
Tim.
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