Add preserver-interface option to spirv-opt (KhronosGroup#5524)

The optimizer is able to preserve the interface variables of the
shaders, but that feature has not been exposed to the command line
tool.

This commit adds an option `--preserve-interface` to spirv-opt that will
cause all calls to ADCE to leave the input and output variables, even if
the variable is unused. It will apply regardless of where the option
appears on the command line.

Fixes KhronosGroup#5522

include/spirv-tools/libspirv.h

@@ -966,9 +966,16 @@ SPIRV_TOOLS_EXPORT bool spvOptimizerRegisterPassFromFlag(
     spv_optimizer_t* optimizer, const char* flag);
 
 // Registers passes specified by length number of flags in an optimizer object.
+// Passes may remove interface variables that are unused.
 SPIRV_TOOLS_EXPORT bool spvOptimizerRegisterPassesFromFlags(
     spv_optimizer_t* optimizer, const char** flags, const size_t flag_count);
 
+// Registers passes specified by length number of flags in an optimizer object.
+// Passes will not remove interface variables.
+SPIRV_TOOLS_EXPORT bool
+spvOptimizerRegisterPassesFromFlagsWhilePreservingTheInterface(
+    spv_optimizer_t* optimizer, const char** flags, const size_t flag_count);
+
 // Optimizes the SPIR-V code of size |word_count| pointed to by |binary| and
 // returns an optimized spv_binary in |optimized_binary|.
 //

include/spirv-tools/optimizer.hpp

@@ -100,8 +100,6 @@ class Optimizer {
   //
   // If |preserve_interface| is true, all non-io variables in the entry point
   // interface are considered live and are not eliminated.
-  // |preserve_interface| should be true if HLSL is generated
-  // from the SPIR-V bytecode.
   Optimizer& RegisterPerformancePasses();
   Optimizer& RegisterPerformancePasses(bool preserve_interface);
 
@@ -111,8 +109,6 @@ class Optimizer {
   //
   // If |preserve_interface| is true, all non-io variables in the entry point
   // interface are considered live and are not eliminated.
-  // |preserve_interface| should be true if HLSL is generated
-  // from the SPIR-V bytecode.
   Optimizer& RegisterSizePasses();
   Optimizer& RegisterSizePasses(bool preserve_interface);
 
@@ -127,8 +123,6 @@ class Optimizer {
   //
   // If |preserve_interface| is true, all non-io variables in the entry point
   // interface are considered live and are not eliminated.
-  // |preserve_interface| should be true if HLSL is generated
-  // from the SPIR-V bytecode.
   Optimizer& RegisterLegalizationPasses();
   Optimizer& RegisterLegalizationPasses(bool preserve_interface);
 
@@ -139,8 +133,13 @@ class Optimizer {
   // error message is emitted to the MessageConsumer object (use
   // Optimizer::SetMessageConsumer to define a message consumer, if needed).
   //
+  // If |preserve_interface| is true, all non-io variables in the entry point
+  // interface are considered live and are not eliminated.
+  //
   // If all the passes are registered successfully, it returns true.
   bool RegisterPassesFromFlags(const std::vector<std::string>& flags);
+  bool RegisterPassesFromFlags(const std::vector<std::string>& flags,
+                               bool preserve_interface);
 
   // Registers the optimization pass associated with |flag|.  This only accepts
   // |flag| values of the form "--pass_name[=pass_args]".  If no such pass
@@ -157,7 +156,11 @@ class Optimizer {
   //
   // --legalize-hlsl: Registers all passes that legalize SPIR-V generated by an
   //                  HLSL front-end.
+  //
+  // If |preserve_interface| is true, all non-io variables in the entry point
+  // interface are considered live and are not eliminated.
   bool RegisterPassFromFlag(const std::string& flag);
+  bool RegisterPassFromFlag(const std::string& flag, bool preserve_interface);
 
   // Validates that |flag| has a valid format.  Strings accepted:
   //

source/opt/optimizer.cpp

@@ -33,6 +33,15 @@
 
 namespace spvtools {
 
+std::vector<std::string> GetVectorOfStrings(const char** strings,
+                                            const size_t string_count) {
+  std::vector<std::string> result;
+  for (uint32_t i = 0; i < string_count; i++) {
+    result.emplace_back(strings[i]);
+  }
+  return result;
+}
+
 struct Optimizer::PassToken::Impl {
   Impl(std::unique_ptr<opt::Pass> p) : pass(std::move(p)) {}
 
@@ -256,8 +265,13 @@ Optimizer& Optimizer::RegisterSizePasses(bool preserve_interface) {
 Optimizer& Optimizer::RegisterSizePasses() { return RegisterSizePasses(false); }
 
 bool Optimizer::RegisterPassesFromFlags(const std::vector<std::string>& flags) {
+  return RegisterPassesFromFlags(flags, false);
+}
+
+bool Optimizer::RegisterPassesFromFlags(const std::vector<std::string>& flags,
+                                        bool preserve_interface) {
   for (const auto& flag : flags) {
-    if (!RegisterPassFromFlag(flag)) {
+    if (!RegisterPassFromFlag(flag, preserve_interface)) {
       return false;
     }
   }
@@ -281,6 +295,11 @@ bool Optimizer::FlagHasValidForm(const std::string& flag) const {
 }
 
 bool Optimizer::RegisterPassFromFlag(const std::string& flag) {
+  return RegisterPassFromFlag(flag, false);
+}
+
+bool Optimizer::RegisterPassFromFlag(const std::string& flag,
+                                     bool preserve_interface) {
   if (!FlagHasValidForm(flag)) {
     return false;
   }
@@ -342,7 +361,7 @@ bool Optimizer::RegisterPassFromFlag(const std::string& flag) {
   } else if (pass_name == "descriptor-scalar-replacement") {
     RegisterPass(CreateDescriptorScalarReplacementPass());
   } else if (pass_name == "eliminate-dead-code-aggressive") {
-    RegisterPass(CreateAggressiveDCEPass());
+    RegisterPass(CreateAggressiveDCEPass(preserve_interface));
   } else if (pass_name == "eliminate-insert-extract") {
     RegisterPass(CreateInsertExtractElimPass());
   } else if (pass_name == "eliminate-local-single-block") {
@@ -513,11 +532,11 @@ bool Optimizer::RegisterPassFromFlag(const std::string& flag) {
   } else if (pass_name == "fix-storage-class") {
     RegisterPass(CreateFixStorageClassPass());
   } else if (pass_name == "O") {
-    RegisterPerformancePasses();
+    RegisterPerformancePasses(preserve_interface);
   } else if (pass_name == "Os") {
-    RegisterSizePasses();
+    RegisterSizePasses(preserve_interface);
   } else if (pass_name == "legalize-hlsl") {
-    RegisterLegalizationPasses();
+    RegisterLegalizationPasses(preserve_interface);
   } else if (pass_name == "remove-unused-interface-variables") {
     RegisterPass(CreateRemoveUnusedInterfaceVariablesPass());
   } else if (pass_name == "graphics-robust-access") {
@@ -1170,13 +1189,19 @@ SPIRV_TOOLS_EXPORT bool spvOptimizerRegisterPassFromFlag(
 
 SPIRV_TOOLS_EXPORT bool spvOptimizerRegisterPassesFromFlags(
     spv_optimizer_t* optimizer, const char** flags, const size_t flag_count) {
-  std::vector<std::string> opt_flags;
-  for (uint32_t i = 0; i < flag_count; i++) {
-    opt_flags.emplace_back(flags[i]);
-  }
+  std::vector<std::string> opt_flags =
+      spvtools::GetVectorOfStrings(flags, flag_count);
+  return reinterpret_cast<spvtools::Optimizer*>(optimizer)
+      ->RegisterPassesFromFlags(opt_flags, false);
+}
 
-  return reinterpret_cast<spvtools::Optimizer*>(optimizer)->
-      RegisterPassesFromFlags(opt_flags);
+SPIRV_TOOLS_EXPORT bool
+spvOptimizerRegisterPassesFromFlagsWhilePreservingTheInterface(
+    spv_optimizer_t* optimizer, const char** flags, const size_t flag_count) {
+  std::vector<std::string> opt_flags =
+      spvtools::GetVectorOfStrings(flags, flag_count);
+  return reinterpret_cast<spvtools::Optimizer*>(optimizer)
+      ->RegisterPassesFromFlags(opt_flags, true);
 }
 
 SPIRV_TOOLS_EXPORT

tools/opt/opt.cpp

@@ -392,6 +392,11 @@ Options (in lexicographical order):)",
                Ensure that the optimizer preserves all bindings declared within
                the module, even when those bindings are unused.)");
   printf(R"(
+  --preserve-interface
+               Ensure that input and output variables are not removed from the
+               shader, even if they are unused. Note that this option applies to
+               all passes that will be run regardless of the order of the flags.)");
+  printf(R"(
   --preserve-spec-constants
                Ensure that the optimizer preserves all specialization constants declared
                within the module, even when those constants are unused.)");
@@ -701,6 +706,7 @@ OptStatus ParseFlags(int argc, const char** argv,
                      spvtools::ValidatorOptions* validator_options,
                      spvtools::OptimizerOptions* optimizer_options) {
   std::vector<std::string> pass_flags;
+  bool preserve_interface = true;
   for (int argi = 1; argi < argc; ++argi) {
     const char* cur_arg = argv[argi];
     if ('-' == cur_arg[0]) {
@@ -790,6 +796,8 @@ OptStatus ParseFlags(int argc, const char** argv,
         validator_options->SetSkipBlockLayout(true);
       } else if (0 == strcmp(cur_arg, "--relax-struct-store")) {
         validator_options->SetRelaxStructStore(true);
+      } else if (0 == strcmp(cur_arg, "--preserve-interface")) {
+        preserve_interface = true;
       } else {
         // Some passes used to accept the form '--pass arg', canonicalize them
         // to '--pass=arg'.
@@ -812,7 +820,7 @@ OptStatus ParseFlags(int argc, const char** argv,
     }
   }
 
-  if (!optimizer->RegisterPassesFromFlags(pass_flags)) {
+  if (!optimizer->RegisterPassesFromFlags(pass_flags, preserve_interface)) {
     return {OPT_STOP, 1};
   }