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/Bitcode/Reader/BitcodeReader.cpp | 29 +++++++++++++++++++++++++---- 1 file changed, 25 insertions(+), 4 deletions(-) (limited to 'llvm/lib/Bitcode/Reader/BitcodeReader.cpp') diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp index 68b36ee..c227226 100644 --- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp +++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp @@ -911,6 +911,14 @@ getDecodedDLLStorageClass(unsigned Val) { } } +static bool getDecodedDSOLocal(unsigned Val) { + switch(Val) { + default: // Map unknown values to preemptable. + case 0: return false; + case 1: return true; + } +} + static GlobalVariable::ThreadLocalMode getDecodedThreadLocalMode(unsigned Val) { switch (Val) { case 0: return GlobalVariable::NotThreadLocal; @@ -2803,7 +2811,7 @@ Error BitcodeReader::parseComdatRecord(ArrayRef Record) { Error BitcodeReader::parseGlobalVarRecord(ArrayRef Record) { // v1: [pointer type, isconst, initid, linkage, alignment, section, // visibility, threadlocal, unnamed_addr, externally_initialized, - // dllstorageclass, comdat, attributes] (name in VST) + // dllstorageclass, comdat, attributes, preemption specifier] (name in VST) // v2: [strtab_offset, strtab_size, v1] StringRef Name; std::tie(Name, Record) = readNameFromStrtab(Record); @@ -2888,13 +2896,18 @@ Error BitcodeReader::parseGlobalVarRecord(ArrayRef Record) { auto AS = getAttributes(Record[12]).getFnAttributes(); NewGV->setAttributes(AS); } + + if (Record.size() > 13) { + NewGV->setDSOLocal(getDecodedDSOLocal(Record[13])); + } + return Error::success(); } Error BitcodeReader::parseFunctionRecord(ArrayRef Record) { // v1: [type, callingconv, isproto, linkage, paramattr, alignment, section, // visibility, gc, unnamed_addr, prologuedata, dllstorageclass, comdat, - // prefixdata] (name in VST) + // prefixdata, personalityfn, preemption specifier] (name in VST) // v2: [strtab_offset, strtab_size, v1] StringRef Name; std::tie(Name, Record) = readNameFromStrtab(Record); @@ -2968,6 +2981,10 @@ Error BitcodeReader::parseFunctionRecord(ArrayRef Record) { if (Record.size() > 14 && Record[14] != 0) FunctionPersonalityFns.push_back(std::make_pair(Func, Record[14] - 1)); + if (Record.size() > 15) { + Func->setDSOLocal(getDecodedDSOLocal(Record[15])); + } + ValueList.push_back(Func); // If this is a function with a body, remember the prototype we are @@ -2984,9 +3001,11 @@ Error BitcodeReader::parseGlobalIndirectSymbolRecord( unsigned BitCode, ArrayRef Record) { // v1 ALIAS_OLD: [alias type, aliasee val#, linkage] (name in VST) // v1 ALIAS: [alias type, addrspace, aliasee val#, linkage, visibility, - // dllstorageclass] (name in VST) + // dllstorageclass, threadlocal, unnamed_addr, + // preemption specifier] (name in VST) // v1 IFUNC: [alias type, addrspace, aliasee val#, linkage, - // visibility, dllstorageclass] (name in VST) + // visibility, dllstorageclass, threadlocal, unnamed_addr, + // preemption specifier] (name in VST) // v2: [strtab_offset, strtab_size, v1] StringRef Name; std::tie(Name, Record) = readNameFromStrtab(Record); @@ -3036,6 +3055,8 @@ Error BitcodeReader::parseGlobalIndirectSymbolRecord( NewGA->setThreadLocalMode(getDecodedThreadLocalMode(Record[OpNum++])); if (OpNum != Record.size()) NewGA->setUnnamedAddr(getDecodedUnnamedAddrType(Record[OpNum++])); + if (OpNum != Record.size()) + NewGA->setDSOLocal(getDecodedDSOLocal(Record[OpNum++])); ValueList.push_back(NewGA); IndirectSymbolInits.push_back(std::make_pair(NewGA, Val)); return Error::success(); -- cgit v1.1