[Coroutines] Schedule coro-split before asan

Summary:
The docs for the LLVM coroutines intrinsic `@llvm.coro.id` state that
"The second argument, if not null, designates a particular alloca instruction
to be a coroutine promise."

However, if the address sanitizer pass is run before the `@llvm.coro.id`
intrinsic is lowered, the `alloca` instruction passed to the intrinsic as its
second argument is converted, as per the
https://github.com/google/sanitizers/wiki/AddressSanitizerAlgorithm docs, to
an `inttoptr` instruction that accesses the address of the promise.

On optimization levels `-O1` and above, the `-asan` pass is run after
`-coro-early`, `-coro-split`, and `-coro-elide`, and before
`-coro-cleanup`, and so there is no issue. At `-O0`, however, `-asan`
is run in between `-coro-early` and `-coro-split`, which causes an
assertion to be hit when the `inttoptr` instruction is forcibly cast to
an `alloca`.

Rearrange the passes such that the coroutine passes are registered
before the sanitizer passes.

Test Plan:
Compile a simple C++ program that uses coroutines in `-O0` with
`-fsanitize-address`, and confirm no assertion is hit:
`clang++ coro-example.cpp -fcoroutines-ts -g -fsanitize=address -fno-omit-frame-pointer`.

Reviewers: GorNishanov, lewissbaker, EricWF

Reviewed By: GorNishanov

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D43927

llvm-svn: 328951

clang/lib/CodeGen/BackendUtil.cpp

@@ -541,6 +541,9 @@ void EmitAssemblyHelper::CreatePasses(legacy::PassManager &MPM,
                            addObjCARCOptPass);
   }
 
+  if (LangOpts.CoroutinesTS)
+    addCoroutinePassesToExtensionPoints(PMBuilder);
+
   if (LangOpts.Sanitize.has(SanitizerKind::LocalBounds)) {
     PMBuilder.addExtension(PassManagerBuilder::EP_ScalarOptimizerLate,
                            addBoundsCheckingPass);
@@ -599,9 +602,6 @@ void EmitAssemblyHelper::CreatePasses(legacy::PassManager &MPM,
                            addDataFlowSanitizerPass);
   }
 
-  if (LangOpts.CoroutinesTS)
-    addCoroutinePassesToExtensionPoints(PMBuilder);
-
   if (LangOpts.Sanitize.hasOneOf(SanitizerKind::Efficiency)) {
     PMBuilder.addExtension(PassManagerBuilder::EP_OptimizerLast,
                            addEfficiencySanitizerPass);