[IRGen] Don't emit coverage maps for synthesized Clang decls

We don't need to perform coverage mapping for any
Clang decls we've synthesized, as they have no
user-written code. This is also needed to avoid a
Clang crash when attempting to emit coverage for
decls without source locations (rdar://100172217).

rdar://82820628

Author: hamishknight

lib/IRGen/IRGenModule.cpp

@@ -138,6 +138,12 @@ static clang::CodeGenerator *createClangCodeGenerator(ASTContext &Context,
     CGO.TrapFuncName = Opts.TrapFuncName;
   }
 
+  // We don't need to perform coverage mapping for any Clang decls we've
+  // synthesized, as they have no user-written code. This is also needed to
+  // avoid a Clang crash when attempting to emit coverage for decls without
+  // source locations (rdar://100172217).
+  CGO.CoverageMapping = false;
+
   auto &VFS = Importer->getClangInstance().getVirtualFileSystem();
   auto &HSI = Importer->getClangPreprocessor()
                   .getHeaderSearchInfo()

test/Profiler/Inputs/issue-57483/cmodule.h

@@ -0,0 +1,3 @@
+struct cstruct {
+  int member : 16;
+};

test/Profiler/Inputs/issue-57483/module.modulemap

@@ -0,0 +1,3 @@
+module CModule {
+  header "cmodule.h"
+}

test/Profiler/issue-57483.swift

@@ -0,0 +1,14 @@
+// RUN: %target-swift-frontend -emit-ir -profile-generate -profile-coverage-mapping -Xcc -fprofile-instr-generate -Xcc -fcoverage-mapping -I %S/Inputs/issue-57483 %s | %FileCheck %s
+
+// https://github.com/apple/swift/issues/57483 (rdar://82820628)
+// Make sure we don't crash in IRGen attempting to emit the coverage map for the
+// implicit Clang getter for the member bitfield.
+
+// CHECK: define {{.*}} @"$So7cstructV$member$getter"
+
+import CModule
+
+func foo(_ x: UnsafePointer<cstruct>?) {
+  _ = x?.pointee.member
+}
+foo(nil)