37561ba89b
`clang -fpic -fno-semantic-interposition` may set dso_local on variables for -fpic. GCC folks consider there are 'address interposition' and 'semantic interposition', and 'disabling semantic interposition' can optimize function calls but cannot change variable references to use local aliases (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100483). This patch removes dso_local for variables in `clang -fpic -fno-semantic-interposition` mode so that the built shared objects can work with copy relocations. Building llvm-project tiself with -fno-semantic-interposition (D102453) should now be safe with trunk Clang. Example: ``` // a.c int var; int *addr() { return var; } // old: cannot be interposed movslq .Lvar$local(%rip), %rax // new: can be interposed movq var@GOTPCREL(%rip), %rax movslq (%rax), %rax ``` The local alias lowering for `GlobalVariable`s is kept in case there is a future option allowing local aliases. Reviewed By: rnk Differential Revision: https://reviews.llvm.org/D102583
39 lines
1.6 KiB
C
39 lines
1.6 KiB
C
/// -fno-semantic-interposition is the default and local aliases (via dso_local) are allowed.
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// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm -mrelocation-model pic -pic-level 1 %s -o - | FileCheck %s --check-prefixes=CHECK,NOMETADATA
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/// -fsemantic-interposition sets a module metadata.
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// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm -mrelocation-model pic -pic-level 1 -fsemantic-interposition %s -o - | FileCheck %s --check-prefixes=PREEMPT,METADATA
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/// Traditional half-baked behavior: interprocedural optimizations are allowed
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/// but local aliases are not used.
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// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm -mrelocation-model pic -pic-level 1 -fhalf-no-semantic-interposition %s -o - | FileCheck %s --check-prefixes=PREEMPT,NOMETADATA
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// CHECK: @var = global i32 0, align 4
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// CHECK: @ext_var = external global i32, align 4
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// CHECK: @ifunc = ifunc i32 (), bitcast (i8* ()* @ifunc_resolver to i32 ()*)
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// CHECK: define dso_local i32 @func()
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// CHECK: declare i32 @ext()
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// PREEMPT: @var = global i32 0, align 4
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// PREEMPT: @ext_var = external global i32, align 4
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// PREEMPT: @ifunc = ifunc i32 (), bitcast (i8* ()* @ifunc_resolver to i32 ()*)
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// PREEMPT: define i32 @func()
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// PREEMPT: declare i32 @ext()
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// METADATA: !{{[0-9]+}} = !{i32 1, !"SemanticInterposition", i32 1}
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// NOMETADATA-NOT: "SemanticInterposition"
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int var;
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extern int ext_var;
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int ifunc(void) __attribute__((ifunc("ifunc_resolver")));
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int func(void) { return 0; }
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int ext(void);
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static void *ifunc_resolver() { return func; }
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int foo() {
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return var + ext_var + ifunc() + func() + ext();
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}
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