[XLA] Add --xla_disable_all_hlo_passes flag.

Previously we only had a flag for disabling specific passes.  But being able to
disable all passes is helpful if you have some already-optimized HLO that you
just want to run.

PiperOrigin-RevId: 224928095

tensorflow/compiler/xla/debug_options_flags.cc

@@ -201,6 +201,16 @@ static void AllocateFlags() {
           "Comma-separated list of hlo passes to be disabled. These names "
           "must exactly match the passes' names; no whitespace around "
           "commas."),
+      tensorflow::Flag(
+          "xla_disable_all_hlo_passes",
+          bool_setter_for(&DebugOptions::set_xla_disable_all_hlo_passes), false,
+          "Disables all HLO passes.  Notes that some passes are necessary for "
+          "correctness and the invariants that must be satisfied by 'fully "
+          "optimized' HLO are different for different devices and may change "
+          "over time.  The only 'guarantee', such as it is, is that if you "
+          "compile XLA and dump the optimized HLO for some graph, you should "
+          "be able to run it again on the same device with the same build of "
+          "XLA."),
       tensorflow::Flag(
           "xla_embed_ir_in_executable",
           bool_setter_for(&DebugOptions::set_xla_embed_ir_in_executable),

tensorflow/compiler/xla/service/hlo_pass_pipeline.cc

@@ -77,6 +77,11 @@ std::vector<HloPassInterface*> HloPassPipeline::GetEnabledPasses(
   auto repeated_field = debug_options.xla_disable_hlo_passes();
   absl::flat_hash_set<string> disabled_pass_names(repeated_field.begin(),
                                                   repeated_field.end());
+  if (debug_options.xla_disable_all_hlo_passes()) {
+    VLOG(1) << "*All* passes disabled by --xla_disable_all_hlo_passes.";
+    return {};
+  }
+
   if (!disabled_pass_names.empty()) {
     VLOG(1) << "Passes disabled by --xla_disable_hlo_passes: "
             << absl::StrJoin(disabled_pass_names, ", ");

tensorflow/compiler/xla/xla.proto

@@ -100,6 +100,14 @@ message DebugOptions {
   // names as specified by the HloPassInterface::name() method.
   repeated string xla_disable_hlo_passes = 30;
 
+  // Disables all HLO passes.  Notes that some passes are necessary for
+  // correctness and the invariants that must be satisfied by "fully optimized"
+  // HLO are different for different devices and may change over time.  The only
+  // "guarantee", such as it is, is that if you compile XLA and dump the
+  // optimized HLO for some graph, you should be able to run it again on the
+  // same device with the same build of XLA.
+  bool xla_disable_all_hlo_passes = 104;
+
   // Numerical optimization level for the XLA compiler backend; the specific
   // interpretation of this value is left to the backends.
   int32 xla_backend_optimization_level = 31;
@@ -216,6 +224,8 @@ message DebugOptions {
   // If set to true XLA:GPU invokes `ptxas` with -O0 (default is -O3).
   bool xla_gpu_disable_ptxas_optimizations = 103;
 
+  // Next id: 105
+
   // Extra options to pass to the compilation backend (e.g. LLVM); specific
   // interpretation of these values is left to the backend.
   map<string, string> xla_backend_extra_options = 500;