[CodeExtractor] Mark functions noreturn when applicable

This eliminates the outlining penalty for llvm.trap/unreachable, because
callers no longer have to emit cleanup/ret instructions after calling an
outlined `noreturn` function.

rdar://45523626

llvm-svn: 346421

2 files changed, 10 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/CodeExtractor.cpp b/llvm/lib/Transforms/Utils/CodeExtractor.cpp
index 419e1db08bf..41c3632c82a 100644
--- a/llvm/lib/Transforms/Utils/CodeExtractor.cpp
+++ b/llvm/lib/Transforms/Utils/CodeExtractor.cpp
@@ -1330,6 +1330,13 @@ Function *CodeExtractor::extractCodeRegion() {
       DVI->eraseFromParent();
   }
 
+  // Mark the new function `noreturn` if applicable.
+  bool doesNotReturn = none_of(*newFunction, [](const BasicBlock &BB) {
+    return isa<ReturnInst>(BB.getTerminator());
+  });
+  if (doesNotReturn)
+    newFunction->setDoesNotReturn();
+
   LLVM_DEBUG(if (verifyFunction(*newFunction))
                  report_fatal_error("verifyFunction failed!"));
   return newFunction;
diff --git a/llvm/test/Transforms/HotColdSplit/split-cold-2.ll b/llvm/test/Transforms/HotColdSplit/split-cold-2.ll
index ac7d856608c..66c6fbb1b8d 100644
--- a/llvm/test/Transforms/HotColdSplit/split-cold-2.ll
+++ b/llvm/test/Transforms/HotColdSplit/split-cold-2.ll
@@ -9,6 +9,9 @@
 ; CHECK: codeRepl:
 ; CHECK-NEXT: call void @fun.cold.1
 
+; CHECK: define {{.*}}@fun.cold.1{{.*}} [[cold_attr:#[0-9]+]]
+; CHECK: attributes [[cold_attr]] = { {{.*}}noreturn
+
 define void @fun() {
 entry:
   br i1 undef, label %if.then, label %if.else