[CFI] Require -flto instead of implying it.

Summary:
This is unfortunate, but would let us land http://reviews.llvm.org/D10467,
that makes ToolChains responsible for computing the set of sanitizers
they support.

Unfortunately, Darwin ToolChains doesn't know about actual OS they
target until ToolChain::TranslateArgs() is called. In particular, it
means we won't be able to construct SanitizerArgs for these ToolChains
before that.

This change removes SanitizerArgs::needsLTO() method, so that now
ToolChain::IsUsingLTO(), which is called very early, doesn't need
SanitizerArgs to implement this method.

Docs and test cases are updated accordingly. See
https://llvm.org/bugs/show_bug.cgi?id=23539, which describes why we
start all these.

Test Plan: regression test suite

Reviewers: pcc

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D10560

llvm-svn: 240170

1 files changed, 3 insertions, 9 deletions

diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index 1c6f4d1e097..0f3ebef2cf2 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -1362,7 +1362,7 @@ Driver::ConstructPhaseAction(const ToolChain &TC, const ArgList &Args,
                                                types::TY_LLVM_BC);
   }
   case phases::Backend: {
-    if (IsUsingLTO(TC, Args)) {
+    if (IsUsingLTO(Args)) {
       types::ID Output =
         Args.hasArg(options::OPT_S) ? types::TY_LTO_IR : types::TY_LTO_BC;
       return llvm::make_unique<BackendJobAction>(std::move(Input), Output);
@@ -1383,14 +1383,8 @@ Driver::ConstructPhaseAction(const ToolChain &TC, const ArgList &Args,
   llvm_unreachable("invalid phase in ConstructPhaseAction");
 }
 
-bool Driver::IsUsingLTO(const ToolChain &TC, const ArgList &Args) const {
-  if (TC.getSanitizerArgs().needsLTO())
-    return true;
-
-  if (Args.hasFlag(options::OPT_flto, options::OPT_fno_lto, false))
-    return true;
-
-  return false;
+bool Driver::IsUsingLTO(const ArgList &Args) const {
+  return Args.hasFlag(options::OPT_flto, options::OPT_fno_lto, false);
 }
 
 void Driver::BuildJobs(Compilation &C) const {