2018-08-23 03:05:19 +08:00
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// RUN: %clang_cc1 -fkeep-static-consts -emit-llvm %s -o - -triple=x86_64-unknown-linux-gnu | FileCheck %s
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// CHECK: @_ZL7srcvers = internal constant [4 x i8] c"xyz\00", align 1
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2018-10-26 03:13:46 +08:00
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// CHECK: @_ZL8srcvers2 = internal constant [4 x i8] c"abc\00", align 1
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// CHECK: @_ZL1N = internal constant i32 2, align 4
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Change some addUsedGlobal to addUsedOrCompilerUsedGlobal
An global value in the `llvm.used` list does not have GC root semantics on ELF targets.
This will be changed in a subsequent backend patch.
Change some `llvm.used` in the ELF code path to use `llvm.compiler.used` to
prevent undesired GC root semantics.
Change one extern "C" alias (due to `__attribute__((used))` in extern "C") to use `llvm.compiler.used` on all targets.
GNU ld has a rule "`__start_/__stop_` references from a live input section retain the associated C identifier name sections",
which LLD may drop entirely (currently refined to exclude SHF_LINK_ORDER/SHF_GROUP) in a future release (the rule makes it clumsy to GC metadata sections; D96914 added a way to try the potential future behavior).
For `llvm.used` global values defined in a C identifier name section, keep using `llvm.used` so that
the future LLD change will not affect them.
rnk kindly categorized the changes:
```
ObjC/blocks: this wants GC root semantics, since ObjC mainly runs on Mac.
MS C++ ABI stuff: wants GC root semantics, no change
OpenMP: unsure, but GC root semantics probably don't hurt
CodeGenModule: affected in this patch to *not* use GC root semantics so that __attribute__((used)) behavior remains the same on ELF, plus two other minor use cases that don't want GC semantics
Coverage: Probably want GC root semantics
CGExpr.cpp: refers to LTO, wants GC root
CGDeclCXX.cpp: one is MS ABI specific, so yes GC root, one is some other C++ init functionality, which should form GC roots (C++ initializers can have side effects and must run)
CGDecl.cpp: Changed in this patch for __attribute__((used))
```
Differential Revision: https://reviews.llvm.org/D97446
2021-02-27 02:42:07 +08:00
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// CHECK: @llvm.compiler.used = appending global [4 x i8*] [i8* getelementptr inbounds ([4 x i8], [4 x i8]* @_ZL7srcvers, i32 0, i32 0), i8* bitcast (i32* @b to i8*), i8* getelementptr inbounds ([4 x i8], [4 x i8]* @_ZL8srcvers2, i32 0, i32 0), i8* bitcast (i32* @_ZL1N to i8*)], section "llvm.metadata"
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2018-10-26 03:13:46 +08:00
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2018-08-23 03:05:19 +08:00
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static const char srcvers[] = "xyz";
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extern const int b = 1;
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2018-10-26 03:13:46 +08:00
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const char srcvers2[] = "abc";
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constexpr int N = 2;
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