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If a local_unnamed_addr attribute is attached to a global, the address is known to be insignificant within the module. It is distinct from the existing unnamed_addr attribute in that it only describes a local property of the module rather than a global property of the symbol. This attribute is intended to be used by the code generator and LTO to allow the linker to decide whether the global needs to be in the symbol table. It is possible to exclude a global from the symbol table if three things are true: - This attribute is present on every instance of the global (which means that the normal rule that the global must have a unique address can be broken without being observable by the program by performing comparisons against the global's address) - The global has linkonce_odr linkage (which means that each linkage unit must have its own copy of the global if it requires one, and the copy in each linkage unit must be the same) - It is a constant or a function (which means that the program cannot observe that the unique-address rule has been broken by writing to the global) Although this attribute could in principle be computed from the module contents, LTO clients (i.e. linkers) will normally need to be able to compute this property as part of symbol resolution, and it would be inefficient to materialize every module just to compute it. See: http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20160509/356401.html http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20160516/356738.html for earlier discussion. Part of the fix for PR27553. Differential Revision: http://reviews.llvm.org/D20348 llvm-svn: 272709
43 lines
1.2 KiB
LLVM
43 lines
1.2 KiB
LLVM
; RUN: llvm-as < %s >%t1
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; RUN: llvm-lto -o %t2 %t1
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; RUN: llvm-nm %t2 | FileCheck %s -check-prefix=NOEXPORT
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; RUN: llvm-lto -o %t3 -exported-symbol=main %t1
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; RUN: llvm-nm %t3 | FileCheck %s -check-prefix=EXPORT
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target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
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target triple = "x86_64-unknown-linux-gnu"
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module asm ".text"
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module asm ".align 16, 0x90"
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module asm ".type PR14512, @function"
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module asm "PR14512:.cfi_startproc"
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module asm "ret"
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module asm ".cfi_endproc"
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declare void @PR14512()
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; Without -exported-symbol, main should be eliminated by LTO.
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; With -exported-symbol=main, main should be preserved by LTO.
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define i32 @main(i32 %argc, i8** %argv) {
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; NOEXPORT-NOT: main
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; EXPORT: main
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call void @PR14512()
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ret i32 0
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}
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; RUN: llvm-lto -o %t -dso-symbol=zed1 -dso-symbol=zed2 %t1 -O0
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; RUN: llvm-nm %t | FileCheck %s -check-prefix=ZED1_AND_ZED2
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; ZED1_AND_ZED2: V zed1
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@zed1 = linkonce_odr global i32 42
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define i32* @get_zed1() {
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ret i32* @zed1
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}
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; ZED1_AND_ZED2: r zed2
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@zed2 = linkonce_odr unnamed_addr constant i32 42
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define i32 @useZed2() {
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%x = load i32, i32* @zed2
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ret i32 %x
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}
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