https://bugs.llvm.org/show_bug.cgi?id=39088
Bug ID: 39088
Summary: __attribute__((alias)) should prevent DCE
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Interprocedural Optimizations
Assignee: unassignedb...@nondot.org
Reporter: ndesaulni...@google.com
CC: george.burgess...@gmail.com, jykni...@google.com,
lloz...@chromium.org, llvm-bugs@lists.llvm.org,
manojgu...@google.com, nir...@google.com,
srhi...@google.com
Consider this test case, from the Linux kernel's heavily used
MODULE_DEVICE_TABLE macro: https://godbolt.org/z/Dpxnbp
static int foo [] = { 42, 0xDEAD };
extern typeof(foo) bar __attribute__((unused, alias("foo")));
At -O2, GCC emits essentially:
.type foo, @object
.size foo, 8
foo:
.long 42
.long 57005
.globl bar
.set bar,fo
Clang with -Wall (and thus -Wunneeded-internal-declaration) warns for
-Wunneeded-internal-declaration, then at -O1 and up produces:
.type bar,@object # @bar
.globl bar
bar:
.long 42 # 0x2a
.long 57005 # 0xdead
.size bar, 8
indeed dropping all references to foo. Removing the `static` type qualifier
can work around this, but it seems that DCE should not remove variables that
are referenced by alias attributes.
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