[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
diff --git a/clang/docs/ControlFlowIntegrity.rst b/clang/docs/ControlFlowIntegrity.rst
index 915385b..ce1c37b 100644
--- a/clang/docs/ControlFlowIntegrity.rst
+++ b/clang/docs/ControlFlowIntegrity.rst
@@ -20,8 +20,8 @@
allowing developers to enable them in release builds.
To enable Clang's available CFI schemes, use the flag ``-fsanitize=cfi``.
-As currently implemented, CFI relies on link-time optimization (LTO); the CFI
-schemes imply ``-flto``, and the linker used must support LTO, for example
+As currently implemented, CFI relies on link-time optimization (LTO); so it is
+required to specify ``-flto``, and the linker used must support LTO, for example
via the `gold plugin`_. To allow the checks to be implemented efficiently,
the program must be structured such that certain object files are compiled
with CFI enabled, and are statically linked into the program. This may