BackendUtil: Pass through -mdisable-tail-calls

The frontend option -fno-optimize-sibling-calls resolves to -cc1's
-mdisable-tail-calls, which is passed to the TargetMachine in the
backend.  PassManagerBuilder was adding the -tailcallelim pass anyway.

Use a new DisableTailCalls option in PassManagerBuilder to disable tail
calls harder.

Requires the matching commit in LLVM that adds DisableTailCalls.

<rdar://problem/16050591>

llvm-svn: 206543

clang/lib/CodeGen/BackendUtil.cpp

@@ -247,6 +247,7 @@ void EmitAssemblyHelper::CreatePasses() {
   PMBuilder.SLPVectorize = CodeGenOpts.VectorizeSLP;
   PMBuilder.LoopVectorize = CodeGenOpts.VectorizeLoop;
 
+  PMBuilder.DisableTailCalls = CodeGenOpts.DisableTailCalls;
   PMBuilder.DisableUnitAtATime = !CodeGenOpts.UnitAtATime;
   PMBuilder.DisableUnrollLoops = !CodeGenOpts.UnrollLoops;
   PMBuilder.RerollLoops = CodeGenOpts.RerollLoops;

clang/test/CodeGen/disable-tail-calls.c

@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.9.0 -emit-llvm -O1 -mdisable-tail-calls -o - < %s | FileCheck %s
+
+typedef struct List {
+  struct List *next;
+  int data;
+} List;
+
+// CHECK-LABEL: define %struct.List* @find
+List *find(List *head, int data) {
+  if (!head)
+    return 0;
+  if (head->data == data)
+    return head;
+  // CHECK: call %struct.List* @find
+  return find(head->next, data);
+}