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[LTO] Inherit options from Codegen before initializing TargetMachine. 

This fixes bootstrap of llvm-tblgen (with LTO) and PR27150.
Slightly longer explanation follows.

Emission of .init_array instead of .ctors is supported only on a
subset of the Target LLVM supports. Codegen needs to be conservative
and always emit .ctors unless instructed otherwise (based on target).
If the dynamic linker sees .init_array it completely ignores
what's inside .ctors and therefore some constructors are not called
(and this causes llvm-tblgen to crash on startup).

Teach LLD/LTO about the Codegen options so we end up always emitting
.init_array and avoid this issue.
In future, we might end up supporting mix of .ctors and .init_array
in different input files if this shows up as a real-world use case.
The way gold handles this case is mapping .ctors from input into
.init_array in output. There's also another caveat because
as far as I understand .ctors run in reverse order so when we do
the copy/mapping we need to reverse copy in the output if there's
more than one ctor. That's why I'd rather avoid this complicate logic
unless there's a real need.

An analogous reasoning holds for .dtors/.fini_array.

llvm-svn: 265085
This commit is contained in:
Davide Italiano 2016-04-01 00:35:29 +00:00
parent e9148dd62f
commit 8eca282dc9
2 changed files with 5 additions and 2 deletions
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3
lld/ELF/LTO.cpp
View File

@ -15,6 +15,7 @@
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/Bitcode/ReaderWriter.h"
#include "llvm/CodeGen/CommandFlags.h"
#include "llvm/IR/LegacyPassManager.h"
#include "llvm/Linker/IRMover.h"
#include "llvm/Support/StringSaver.h"
@ -167,7 +168,7 @@ TargetMachine *BitcodeCompiler::getTargetMachine() {
const Target *T = TargetRegistry::lookupTarget(TripleStr, Msg);
if (!T)
fatal("target not found: " + Msg);
TargetOptions Options;
TargetOptions Options = InitTargetOptionsFromCodeGenFlags();
Reloc::Model R = Config->Pic ? Reloc::PIC_ : Reloc::Static;
return T->createTargetMachine(TripleStr, "", "", Options, R);
}

4
lld/test/ELF/lto/ctors.ll
View File

@ -13,4 +13,6 @@ define void @ctor() {
}
; The llvm.global_ctors should end up producing constructors.
; CHECK: Name: .ctors
; On x86-64 (linux) we should always emit .init_array and never .ctors.
; CHECK: Name: .init_array
; CHECK-NOT: Name: .ctors