[DebugInfo] Don't emit debug info for async suspend/dispatch functions

Those functions are effectively outlined functions with an alwaysinline
attribute. By removing their debug info and relying on the inliner to propagate
the call site location to the inlined instructions, we restore the "original"
locations as if the function had never been outlined.

This is technically relying on an implementation detail of the inliner, but it
seems to be the simplest way of addressing this issue.

Author: felipepiovezan

lib/IRGen/GenFunc.cpp

@@ -2899,9 +2899,6 @@ IRGenFunction::createAsyncDispatchFn(const FunctionPointer &fnPtr,
   dispatch->setDoesNotThrow();
   dispatch->addFnAttr(llvm::Attribute::AlwaysInline);
   IRGenFunction dispatchIGF(IGM, dispatch);
-  // Don't emit debug info if we are generating a function for the prologue.
-  if (IGM.DebugInfo && Builder.getCurrentDebugLocation())
-    IGM.DebugInfo->emitOutlinedFunction(dispatchIGF, dispatch, CurFn->getName());
   auto &Builder = dispatchIGF.Builder;
   auto it = dispatchIGF.CurFn->arg_begin(), end = dispatchIGF.CurFn->arg_end();
   llvm::Value *fnPtrArg = &*(it++);
@@ -2987,9 +2984,6 @@ llvm::Function *IRGenFunction::createAsyncSuspendFn() {
   suspendFn->setDoesNotThrow();
   suspendFn->addFnAttr(llvm::Attribute::AlwaysInline);
   IRGenFunction suspendIGF(IGM, suspendFn);
-  if (IGM.DebugInfo)
-    IGM.DebugInfo->emitOutlinedFunction(suspendIGF, suspendFn,
-                                        CurFn->getName());
   auto &Builder = suspendIGF.Builder;
 
   llvm::Value *resumeFunction = suspendFn->getArg(0);

test/DebugInfo/async-await-no-debug-info-outlined-funcs.swift

@@ -0,0 +1,43 @@
+// RUN: %target-swift-frontend %s -emit-irgen -g -o - \
+// RUN:    -module-name M  -disable-availability-checking \
+// RUN:    -parse-as-library | %FileCheck %s --check-prefix=CHECK
+
+// REQUIRES: concurrency
+
+// Check that all the helper "outlined" functions do not have debug information.
+
+func ASYNC___1___() async -> Int {
+  return 42
+}
+
+func ASYNC___2___() async -> Int {
+  print("hello")
+  var x = await ASYNC___1___()
+  x += await ASYNC___1___()
+  return x
+}
+
+// CHECK-LABEL: define {{.*}} @"$s1M12ASYNC___1___SiyYaF.0"
+// CHECK-NOT: !dbg
+// CHECK: ret void
+// CHECK-NEXT: }
+
+// CHECK-LABEL: define {{.*}} @"$s1M12ASYNC___2___SiyYaF.1"
+// CHECK-NOT: !dbg
+// CHECK: ret void
+// CHECK-NEXT: }
+
+// CHECK-LABEL: define {{.*}} @"$s1M12ASYNC___2___SiyYaF.0"
+// CHECK-NOT: !dbg
+// CHECK: ret void
+// CHECK-NEXT: }
+
+// CHECK-LABEL: define {{.*}} @"$s1M12ASYNC___2___SiyYaF.0.1"
+// CHECK-NOT: !dbg
+// CHECK: ret void
+// CHECK-NEXT: }
+
+// CHECK-LABEL: define {{.*}} @"$s1M12ASYNC___2___SiyYaF.0.2"
+// CHECK-NOT: !dbg
+// CHECK: ret void
+// CHECK-NEXT: }

test/IRGen/async/get_async_continuation.sil

@@ -69,11 +69,10 @@ bb0:
 // CHECK:      {{musttail call swifttailcc|tail call swiftcc}} void @swift_continuation_await(ptr %0)
 // CHECK-NEXT: ret void
 
-// CHECK: define {{.*}} void @async_continuation.0(ptr %0, ptr %1){{.*}}!dbg ![[DBG:[0-9]+]]
+// CHECK: define {{.*}} void @async_continuation.0(ptr %0, ptr %1)
 // CHECK-NOT: define
 // CHECK:  tail call swift{{(tail)?}}cc void %{{.*}}(ptr swiftasync %1)
 // CHECK-NEXT:  ret void
-// CHECK: ![[DBG]] = distinct !DISubprogram(linkageName: "async_continuation"
 
 sil @async_continuation : $@async () -> () {
 entry: