[SILProfiler] Set up profiling for lazily-emitted functions (#22403)

A SIL function that's initially only emitted as a declaration may later
be prepared for definition. When this happens, set up a profiler for the
definition.

This makes code coverage visible for private methods (the frontend
follows a declare-then-define pattern for these).

rdar://47759243

Author: vedantk

lib/SILGen/SILGen.cpp

@@ -606,20 +606,12 @@ SILGenModule::getOrCreateProfilerForConstructors(DeclContext *ctx,
   return profiler;
 }
 
-SILFunction *SILGenModule::getFunction(SILDeclRef constant,
-                                       ForDefinition_t forDefinition) {
-  // If we already emitted the function, return it (potentially preparing it
-  // for definition).
-  if (auto emitted = getEmittedFunction(constant, forDefinition))
-    return emitted;
-
-  // Note: Do not provide any SILLocation. You can set it afterwards.
-  SILGenFunctionBuilder builder(*this);
-  auto *F = builder.getOrCreateFunction(constant.hasDecl() ? constant.getDecl()
-                                                           : (Decl *)nullptr,
-                                        constant, forDefinition);
+/// Set up the function for profiling instrumentation.
+static void setUpForProfiling(SILDeclRef constant, SILFunction *F,
+                              ForDefinition_t forDefinition) {
+  if (!forDefinition)
+    return;
 
-  // Set up the function for profiling instrumentation.
   ASTNode profiledNode;
   if (!haveProfiledAssociatedFunction(constant)) {
     if (constant.hasDecl()) {
@@ -637,6 +629,23 @@ SILFunction *SILGenModule::getFunction(SILDeclRef constant,
     if (SILProfiler *SP = F->getProfiler())
       F->setEntryCount(SP->getExecutionCount(profiledNode));
   }
+}
+
+SILFunction *SILGenModule::getFunction(SILDeclRef constant,
+                                       ForDefinition_t forDefinition) {
+  // If we already emitted the function, return it (potentially preparing it
+  // for definition).
+  if (auto emitted = getEmittedFunction(constant, forDefinition)) {
+    setUpForProfiling(constant, emitted, forDefinition);
+    return emitted;
+  }
+
+  // Note: Do not provide any SILLocation. You can set it afterwards.
+  SILGenFunctionBuilder builder(*this);
+  auto *F = builder.getOrCreateFunction(constant.hasDecl() ? constant.getDecl()
+                                                           : (Decl *)nullptr,
+                                        constant, forDefinition);
+  setUpForProfiling(constant, F, forDefinition);
 
   assert(F && "SILFunction should have been defined");
 

test/Profiler/coverage_private.swift

@@ -0,0 +1,14 @@
+// RUN: %target-swift-frontend -Xllvm -sil-full-demangle -profile-generate -profile-coverage-mapping -emit-sorted-sil -emit-sil -module-name coverage_private %s | %FileCheck %s
+
+struct S {
+  func visible() {
+    hidden()
+  }
+
+  // CHECK-LABEL: sil_coverage_map {{.*}}// coverage_private.S.(hidden in {{.*}})() -> ()
+  // CHECK-NEXT:  [[@LINE+1]]:25 -> [[@LINE+2]]:4 : 0
+  private func hidden() {
+  }
+}
+
+S().visible()

test/Profiler/coverage_smoke.swift

@@ -189,4 +189,20 @@ let _ = Class3()
 let _ = Struct1(field: 1)
 let _ = Struct1()
 
+struct Struct2 {
+  func visible() {
+    hidden()
+  }
+  private func hidden() {
+    var x: Int = 0 // CHECK-COV: {{ *}}[[@LINE]]|{{ *}}1
+    func helper() {
+      x += 1 // CHECK-COV: {{ *}}[[@LINE]]|{{ *}}1
+    }
+    helper() // CHECK-COV: {{ *}}[[@LINE]]|{{ *}}1
+  }
+}
+
+var s2 = Struct2()
+s2.visible()
+
 // CHECK-REPORT: TOTAL {{.*}} 100.00% {{.*}} 100.00%