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Move -fno-semantic-interposition dso_local logic from TargetMachine to Clang CodeGenModule

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This simplifies TargetMachine::shouldAssumeDSOLocal and and gives frontend the
decision to use dso_local. For LLVM synthesized functions/globals, they may lose
inferred dso_local but such optimizations are probably not very useful.

Note: the hasComdat() condition in canBenefitFromLocalAlias (D77429) may be dead now.
(llvm/CodeGen/X86/semantic-interposition-comdat.ll)
(Investigate whether we need test coverage when Fuchsia C++ ABI is clearer)
This commit is contained in:
Fangrui Song 2020-12-29 23:37:55 -08:00
parent 14a409567f
commit 28b6140818
3 changed files with 0 additions and 82 deletions
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8
lib/Target/TargetMachine.cpp
View File

@ -163,14 +163,6 @@ bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
// If the symbol is defined, it cannot be preempted. // If the symbol is defined, it cannot be preempted.
if (!GV->isDeclarationForLinker()) if (!GV->isDeclarationForLinker())
return true; return true;
} else if (TT.isOSBinFormatELF()) {
// If dso_local allows AsmPrinter::getSymbolPreferLocal to use a local
// alias, set the flag. We cannot set dso_local for other global values,
// because otherwise direct accesses to a probably interposable symbol (even
// if the codegen assumes not) will be rejected by the linker.
if (!GV->canBenefitFromLocalAlias())
return false;
return TT.isX86() && M.noSemanticInterposition();
} }
// ELF & wasm support preemption of other symbols. // ELF & wasm support preemption of other symbols.

28
test/CodeGen/X86/semantic-interposition-comdat.ll
View File

@ -1,28 +0,0 @@
; RUN: llc -mtriple=x86_64 -relocation-model=pic < %s | FileCheck %s
$comdat_func = comdat any
; CHECK-LABEL: func2:
; CHECK-NOT: .Lfunc2$local
declare void @func()
define hidden void @func2() {
entry:
call void @func()
ret void
}
; CHECK: comdat_func:
; CHECK-NOT: .Lcomdat_func$local
define hidden void @comdat_func() comdat {
entry:
call void @func()
ret void
}
!llvm.module.flags = !{!0, !1}
!0 = !{i32 1, !"SemanticInterposition", i32 0}
!1 = !{i32 7, !"PIC Level", i32 2}

46
test/CodeGen/X86/semantic-interposition-infer-dsolocal.ll
View File

@ -1,46 +0,0 @@
; RUN: llc -mtriple=x86_64 -relocation-model=pic < %s | FileCheck %s
;; With a module flag SemanticInterposition=0, infer dso_local flags even if PIC.
;; Local aliases will be generated for applicable variables and functions.
@var = global i32 0, align 4
@ifunc = ifunc i32 (), bitcast (i32 ()* ()* @ifunc_resolver to i32 ()*)
define i32 @ifunc_impl() {
entry:
ret i32 0
}
define i32 ()* @ifunc_resolver() {
entry:
ret i32 ()* @ifunc_impl
}
declare i32 @external()
define i32 @func() {
ret i32 0
}
;; Don't set dso_local on declarations or ifuncs.
define i32 @foo() {
; CHECK: movl .Lvar$local(%rip), %ebp
; CHECK: callq external@PLT
; CHECK: callq ifunc@PLT
; CHECK: callq .Lfunc$local{{$}}
entry:
%0 = load i32, i32* @var, align 4
%call = tail call i32 @external()
%add = add nsw i32 %call, %0
%call1 = tail call i32 @ifunc()
%add2 = add nsw i32 %add, %call1
%call2 = tail call i32 @func()
%add3 = add nsw i32 %add, %call2
ret i32 %add3
}
!llvm.module.flags = !{!0, !1}
!0 = !{i32 1, !"SemanticInterposition", i32 0}
!1 = !{i32 7, !"PIC Level", i32 2}