From c70d28bff522332b0db2a7466b627fd4cff7c55d Mon Sep 17 00:00:00 2001 From: Sean Fertile Date: Thu, 26 Oct 2017 15:00:26 +0000 Subject: Represent runtime preemption in the IR. 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 --- llvm/lib/Target/TargetMachine.cpp | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'llvm/lib/Target/TargetMachine.cpp') diff --git a/llvm/lib/Target/TargetMachine.cpp b/llvm/lib/Target/TargetMachine.cpp index 3b16dee5a0f..dd6c288607c 100644 --- a/llvm/lib/Target/TargetMachine.cpp +++ b/llvm/lib/Target/TargetMachine.cpp @@ -128,7 +128,8 @@ bool TargetMachine::shouldAssumeDSOLocal(const Module &M, if (TT.isOSBinFormatCOFF() || (TT.isOSWindows() && TT.isOSBinFormatMachO())) return true; - if (GV && (GV->hasLocalLinkage() || !GV->hasDefaultVisibility())) + if (GV && (GV->hasLocalLinkage() || !GV->hasDefaultVisibility() || + GV->isDSOLocal())) return true; if (TT.isOSBinFormatMachO()) { -- cgit v1.2.3