clang: Allow backend unsupported warnings

[arsenm]

Summary

Currently this asserts on anything other than errors. In one
workaround scenario, AMDGPU emits DiagnosticInfoUnsupported as a
warning for functions that can't be correctly codegened, but should
never be executed.

[yaxunl]

LGTM. Thanks.

[arsenm]

5c03beefa720bddb3e3f53c595a76bce7ad50f37

clang/include/clang/Basic/DiagnosticFrontendKinds.td

def remark_fe_backend_optimization_remark_analysis_aliasing : Remark<"%0; "
     "Erroneous results will occur if these options are incorrectly applied!">,
     BackendInfo, InGroup<BackendOptimizationRemarkAnalysis>;
 def warn_fe_backend_optimization_failure : Warning<"%0">, BackendInfo,
     InGroup<BackendOptimizationFailure>, DefaultWarn;
 def note_fe_backend_invalid_loc : Note<"could "
   "not determine the original source location for %0:%1:%2">, BackendInfo;
 
 def err_fe_backend_unsupported : Error<"%0">, BackendInfo;
+def warn_fe_backend_unsupported : Warning<"%0">, BackendInfo;
 
 def err_fe_invalid_code_complete_file : Error<
     "cannot locate code-completion file %0">, DefaultFatal;
 def err_fe_dependency_file_requires_MT : Error<
     "-dependency-file requires at least one -MT or -MQ option">;
 def err_fe_invalid_plugin_name : Error<
     "unable to find plugin '%0'">;
 def err_fe_expected_compiler_job : Error<

clang/lib/CodeGen/CodeGenAction.cpp

if (DILoc.isInvalid() && D.isLocationAvailable())
     Diags.Report(Loc, diag::note_fe_backend_invalid_loc)
         << Filename << Line << Column;
 
   return Loc;
 }
 
 void BackendConsumer::UnsupportedDiagHandler(
     const llvm::DiagnosticInfoUnsupported &D) {
-  // We only support errors.
-  assert(D.getSeverity() == llvm::DS_Error);
+  // We only support warnings or errors.
+  assert(D.getSeverity() == llvm::DS_Error ||
+         D.getSeverity() == llvm::DS_Warning);
 
   StringRef Filename;
   unsigned Line, Column;
   bool BadDebugInfo = false;
   FullSourceLoc Loc;
   std::string Msg;
   raw_string_ostream MsgStream(Msg);
 
   // Context will be nullptr for IR input files, we will construct the diag
   // message from llvm::DiagnosticInfoUnsupported.
   if (Context != nullptr) {
     Loc = getBestLocationFromDebugLoc(D, BadDebugInfo, Filename, Line, Column);
     MsgStream << D.getMessage();
   } else {
     DiagnosticPrinterRawOStream DP(MsgStream);
     D.print(DP);
   }
-  Diags.Report(Loc, diag::err_fe_backend_unsupported) << MsgStream.str();
+
+  auto DiagType = D.getSeverity() == llvm::DS_Error
+                      ? diag::err_fe_backend_unsupported
+                      : diag::warn_fe_backend_unsupported;
+  Diags.Report(Loc, DiagType) << MsgStream.str();
 
   if (BadDebugInfo)
     // If we were not able to translate the file:line:col information
     // back to a SourceLocation, at least emit a note stating that
     // we could not translate this location. This can happen in the
     // case of #line directives.
     Diags.Report(Loc, diag::note_fe_backend_invalid_loc)
         << Filename << Line << Column;

clang/test/CodeGenOpenCL/backend-unsupported-warning.ll

+; RUN: %clang_cc1 -triple amdgcn-amd-amdhsa -S -o - %s 2>&1 | FileCheck %s
+
+; Check that a DiagnosticUnsupported reported as a warning works
+; correctly, and is not emitted as an error.
+
+; CHECK: warning: test.c:2:20: in function use_lds_global_in_func i32 (): local memory global used by non-kernel function
+
+target triple = "amdgcn-amd-amdhsa"
+
+@lds = external addrspace(3) global i32, align 4
+
+define i32 @use_lds_global_in_func() !dbg !5 {
+  %load = load i32, i32 addrspace(3)* @lds, !dbg !9
+  ret i32 %load, !dbg !10
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 3.9.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "test.c", directory: "")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = distinct !DISubprogram(name: "bar", scope: !1, file: !1, line: 2, type: !6, scopeLine: 2, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !2)
+!6 = !DISubroutineType(types: !7)
+!7 = !{!8}
+!8 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
+!9 = !DILocation(line: 2, column: 20, scope: !5)
+!10 = !DILocation(line: 2, column: 13, scope: !5)