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6a96e17cac
Currently we do not represent runtime preemption in the IR, which has several
drawbacks:
1) The semantics of GlobalValues differ depending on the object file format
you are targeting (as well as the relocation-model and -fPIE value).
2) We have no way of disabling inlining of run time interposable functions,
since in the IR we only know if a function is link-time interposable.
Because of this llvm cannot support elf-interposition semantics.
3) In LTO builds of executables we will have extra knowledge that a symbol
resolved to a local definition and can't be preemptable, but have no way to
propagate that knowledge through the compiler.
This patch adds preemptability specifiers to the IR with the following meaning:
dso_local --> means the compiler may assume the symbol will resolve to a
definition within the current linkage unit and the symbol may be accessed
directly even if the definition is not within this compilation unit.
dso_preemptable --> means that the compiler must assume the GlobalValue may be
replaced with a definition from outside the current linkage unit at runtime.
To ease transitioning dso_preemptable is treated as a 'default' in that
low-level codegen will still do the same checks it did previously to see if a
symbol should be accessed indirectly. Eventually when IR producers emit the
specifiers on all Globalvalues we can change dso_preemptable to mean 'always
access indirectly', and remove the current logic.
Differential Revision: https://reviews.llvm.org/D20217
llvm-svn: 316668
48 lines
1.6 KiB
LLVM
48 lines
1.6 KiB
LLVM
; RUN: llvm-as < %s | llvm-dis | FileCheck %s
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; Tests parsing for the dso_local keyword as well as the serialization/
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; deserialization of the dso_local value on GlobalValues.
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@local_global = dso_local global i32 0
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; CHECK: @local_global = dso_local global i32 0
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@weak_local_global = weak dso_local global i32 0
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; CHECK: @weak_local_global = weak dso_local global i32 0
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@external_local_global = external dso_local global i32
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; CHECK: @external_local_global = external dso_local global i32
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@default_local_global = dso_local default global i32 0
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; CHECK: @default_local_global = dso_local global i32 0
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@hidden_local_global = dso_local hidden global i32 0
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; CHECK: @hidden_local_global = dso_local hidden global i32 0
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@protected_local_global = dso_local protected global i32 0
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; CHECK: @protected_local_global = dso_local protected global i32 0
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@local_alias = dso_local alias i32, i32* @local_global
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; CHECK-DAG: @local_alias = dso_local alias i32, i32* @local_global
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@preemptable_alias = dso_preemptable alias i32, i32* @hidden_local_global
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; CHECK-DAG: @preemptable_alias = alias i32, i32* @hidden_local_global
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@preemptable_ifunc = dso_preemptable ifunc void (), i8* ()* @ifunc_resolver
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; CHECK-DAG: @preemptable_ifunc = ifunc void (), i8* ()* @ifunc_resolver
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declare dso_local default void @default_local()
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; CHECK: declare dso_local void @default_local()
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declare dso_local hidden void @hidden_local()
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; CHECK: declare dso_local hidden void @hidden_local()
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define dso_local protected void @protected_local() {
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; CHECK: define dso_local protected void @protected_local()
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entry:
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ret void
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}
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define i8* @ifunc_resolver() {
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entry:
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ret i8* null
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}
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