28cb620321
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
22 lines
565 B
C
22 lines
565 B
C
// RUN: %clang_cc1 -emit-llvm -triple x86_64 %s -o - | FileCheck %s --check-prefixes=CHECK,CUSED
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// RUN: %clang_cc1 -emit-llvm -triple x86_64-apple-darwin %s -o - | FileCheck %s --check-prefixes=CHECK,USED
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// USED: @llvm.used =
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// CUSED: @llvm.compiler.used =
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// CHECK-SAME: @f0
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// CHECK-SAME: @f1.l0
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// CHECK-SAME: @g0
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// CHECK-SAME: @a0
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int g0 __attribute__((used));
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static void __attribute__((used)) f0(void) {
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}
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void f1() {
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static int l0 __attribute__((used)) = 5225;
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}
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__attribute__((used)) int a0;
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void pr27535() { (void)a0; }
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