Add option to force disabling debug info (#4645)

This is (admittedly) a little hacky. DXC spends a lot of compile time
updating debug information because we always generate it so that we can
generate diagnostics for late-running validation.

This patch adds a new flag -fdisable-loc-tracking, which disables
generating debug locations if the user is not generating debug info.

This flag results in about a 15% compile time improvement on a pessimistic
test case. YMMV.

include/dxc/Support/HLSLOptions.h

@@ -205,6 +205,7 @@ public:
   unsigned ScanLimit = 0; // OPT_memdep_block_scan_limit
   bool ForceZeroStoreLifetimes = false; // OPT_force_zero_store_lifetimes
   bool EnableLifetimeMarkers = false; // OPT_enable_lifetime_markers
+  bool ForceDisableLocTracking = false; // OPT_fdisable_loc_tracking
   bool EnableTemplates = false; // OPT_enable_templates
   bool EnableOperatorOverloading = false; // OPT_enable_operator_overloading
   bool StrictUDTCasting = false; // OPT_strict_udt_casting

include/dxc/Support/HLSLOptions.td

@@ -168,6 +168,10 @@ def opt_enable : Separate<["-", "/"], "opt-enable">, Group<hlsloptz_Group>, Flag
 def opt_select : MultiArg<["-", "/"], "opt-select", 2>, MetaVarName<"<opt> <variant>">, Group<hlsloptz_Group>, Flags<[CoreOption, DriverOption, HelpHidden]>,
   HelpText<"Select this optimization variant.">;
 
+def fdisable_loc_tracking : Flag<["-"], "fdisable-loc-tracking">,
+  Group<hlslcomp_Group>, Flags<[CoreOption]>,
+  HelpText<"Disable source location tracking in IR. This will break diagnostic generation for late validation. (Ignored if /Zi is passed)">;
+
 /*
 def fno_caret_diagnostics : Flag<["-"], "fno-caret-diagnostics">, Group<hlslcomp_Group>,
  Flags<[CoreOption]>;

lib/DxcSupport/HLSLOptions.cpp

@@ -828,6 +828,8 @@ int ReadDxcOpts(const OptTable *optionTable, unsigned flagsToInclude,
   opts.EnableLifetimeMarkers = Args.hasFlag(OPT_enable_lifetime_markers, OPT_INVALID,
                                             DXIL::CompareVersions(Major, Minor, 6, 6) >= 0) &&
                               !Args.hasFlag(OPT_disable_lifetime_markers, OPT_INVALID, false);
+  opts.ForceDisableLocTracking =
+      Args.hasFlag(OPT_fdisable_loc_tracking, OPT_INVALID, false);
   opts.EnablePayloadQualifiers = Args.hasFlag(OPT_enable_payload_qualifiers, OPT_INVALID,
                                             DXIL::CompareVersions(Major, Minor, 6, 7) >= 0); 
 

tools/clang/lib/CodeGen/CodeGenAction.cpp

@@ -561,6 +561,13 @@ BackendConsumer::DxilDiagHandler(const llvm::DiagnosticInfoDxil &D) {
     auto *func = D.getFunction();
     if (DiagClient && func)
       DiagClient->setPrefix("Function: " + func->getName().str());
+    
+    // Clang will de-duplicate this so that it only emits once.
+    Diags.Report(
+        Diags.getCustomDiagID(DiagnosticsEngine::Note,
+                              "Debug information is disabled which may impact "
+                              "diagnostic location accuracy. Re-run without "
+                              "-fdisable-loc-tracking to improve accuracy.\n"));
   }
   Diags.Report(Loc, DiagID).AddString(Message);
 

tools/clang/test/HLSLFileCheck/validation/ResourceResolvingNoDI.hlsl

@@ -0,0 +1,25 @@
+// RUN: %dxc -T cs_6_0 -fdisable-loc-tracking %s 2>&1 | FileCheck %s
+
+// CHECK: Function: main: note: Debug information is disabled which may impact diagnostic location accuracy. Re-run without -fdisable-loc-tracking to improve accuracy.
+// CHECK-NOT: note: Debug information is disabled
+
+RWBuffer<int> Buf[2];
+RWBuffer<int> Out;
+
+int getVal(bool B, int Idx) {
+  RWBuffer<int> Local;
+  if (B) Local = Buf[Idx];
+  return Local[Idx];
+}
+
+int getValASecondTime(bool B, int Idx) {
+  RWBuffer<int> Local;
+  if (B) Local = Buf[Idx];
+  return Local[Idx];
+}
+
+[numthreads(1,1,1)]
+void main(uint GI : SV_GroupIndex) {
+  Out[GI] = getVal(false, GI);
+  Out[GI+1] = getValASecondTime(false, GI);
+}

tools/clang/tools/dxcompiler/dxcompilerobj.cpp

@@ -1423,7 +1423,7 @@ public:
       // TODO: consider
       // DebugPass, DebugCompilationDir, DwarfDebugFlags, SplitDwarfFile
     }
-    else {
+    else if (!Opts.ForceDisableLocTracking) {
       CodeGenOptions &CGOpts = compiler.getCodeGenOpts();
       CGOpts.setDebugInfo(CodeGenOptions::LocTrackingOnly);
       CGOpts.DebugColumnInfo = 1;