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//===- ExpandTlsConstantExpr.cpp - Convert ConstantExprs to Instructions---===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass is a helper used by the ExpandTls pass.
//
// LLVM treats the address of a TLS variable as a ConstantExpr. This
// is arguably a bug because the address of a TLS variable is *not* a
// constant: it varies between threads.
//
// See http://llvm.org/bugs/show_bug.cgi?id=14353
//
// This is also a problem for the ExpandTls pass, which wants to use
// replaceUsesOfWith() to replace each TLS variable with an
// Instruction sequence that calls @llvm.nacl.read.tp(). This doesn't
// work if the TLS variable is used inside other ConstantExprs,
// because ConstantExprs are interned and are not associated with any
// function, whereas each Instruction must be part of a function.
//
// To fix that problem, this pass converts ConstantExprs that
// reference TLS variables into Instructions.
//
// For example, this use of a 'ptrtoint' ConstantExpr:
//
// ret i32 ptrtoint (i32* @tls_var to i32)
//
// is converted into this 'ptrtoint' Instruction:
//
// %expanded = ptrtoint i32* @tls_var to i32
// ret i32 %expanded
//
//===----------------------------------------------------------------------===//
#include <vector>
#include "llvm/Pass.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Module.h"
#include "llvm/Transforms/NaCl.h"
using namespace llvm;
namespace {
class ExpandTlsConstantExpr : public ModulePass {
public:
static char ID; // Pass identification, replacement for typeid
ExpandTlsConstantExpr() : ModulePass(ID) {
initializeExpandTlsConstantExprPass(*PassRegistry::getPassRegistry());
}
virtual bool runOnModule(Module &M);
};
}
char ExpandTlsConstantExpr::ID = 0;
INITIALIZE_PASS(ExpandTlsConstantExpr, "nacl-expand-tls-constant-expr",
"Eliminate ConstantExpr references to TLS variables",
false, false)
// This removes ConstantExpr references to the given Constant.
static void expandConstExpr(Constant *Expr) {
// First, ensure that ConstantExpr references to Expr are converted
// to Instructions so that we can modify them.
for (Value::use_iterator UI = Expr->use_begin();
UI != Expr->use_end();
++UI) {
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(*UI)) {
expandConstExpr(CE);
}
}
Expr->removeDeadConstantUsers();
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Expr)) {
while (!Expr->use_empty()) {
Use *U = &Expr->use_begin().getUse();
Instruction *NewInst = CE->getAsInstruction();
NewInst->insertBefore(PhiSafeInsertPt(U));
NewInst->setName("expanded");
PhiSafeReplaceUses(U, NewInst);
}
}
}
bool ExpandTlsConstantExpr::runOnModule(Module &M) {
for (Module::alias_iterator Iter = M.alias_begin();
Iter != M.alias_end(); ) {
GlobalAlias *GA = Iter++;
if (GA->isThreadDependent()) {
GA->replaceAllUsesWith(GA->getAliasee());
GA->eraseFromParent();
}
}
for (Module::global_iterator Global = M.global_begin();
Global != M.global_end();
++Global) {
if (Global->isThreadLocal()) {
expandConstExpr(Global);
}
}
return true;
}
ModulePass *llvm::createExpandTlsConstantExprPass() {
return new ExpandTlsConstantExpr();
}
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