[SPIR-V] Add fspv-preserve-bindings option to preserve decoration bin… (#5211)

* [SPIR-V] Add fspv-preserve-bindings option to preserve decoration bindings even when unused

* Set preserve bindings option in SpirvEmitter::spirvToolsLegalize() also

include/dxc/Support/HLSLOptions.td

@@ -392,6 +392,8 @@ def fspv_print_all: Flag<["-"], "fspv-print-all">, Group<spirv_Group>, Flags<[Co
   HelpText<"Print the SPIR-V module before each pass and after the last one. Useful for debugging SPIR-V legalization and optimization passes.">;
 def Oconfig : CommaJoined<["-"], "Oconfig=">, Group<spirv_Group>, Flags<[CoreOption]>,
   HelpText<"Specify a comma-separated list of SPIRV-Tools passes to customize optimization configuration (see http://khr.io/hlsl2spirv#optimization)">;
+def fspv_preserve_bindings : Flag<["-"], "fspv-preserve-bindings">, Group<spirv_Group>, Flags<[CoreOption, DriverOption]>,
+  HelpText<"Preserves all bindings declared within the module, even when those bindings are unused">;
 // SPIRV Change Ends
 
 //////////////////////////////////////////////////////////////////////////////

include/dxc/Support/SPIRVOptions.h

@@ -55,6 +55,7 @@ struct SpirvCodeGenOptions {
   bool invertW; // Multiplicative inverse
   bool noWarnEmulatedFeatures;
   bool noWarnIgnoredFeatures;
+  bool preserveBindings;
   bool useDxLayout;
   bool useGlLayout;
   bool useLegacyBufferMatrixOrder;

lib/DxcSupport/HLSLOptions.cpp

@@ -985,6 +985,8 @@ int ReadDxcOpts(const OptTable *optionTable, unsigned flagsToInclude,
   opts.SpirvOptions.autoShiftBindings = Args.hasFlag(OPT_fvk_auto_shift_bindings, OPT_INVALID, false);
   opts.SpirvOptions.finiteMathOnly =
       Args.hasFlag(OPT_ffinite_math_only, OPT_fno_finite_math_only, false);
+  opts.SpirvOptions.preserveBindings =
+      Args.hasFlag(OPT_fspv_preserve_bindings, OPT_INVALID, false);
 
   if (!handleVkShiftArgs(Args, OPT_fvk_b_shift, "b", &opts.SpirvOptions.bShift, errors) ||
       !handleVkShiftArgs(Args, OPT_fvk_t_shift, "t", &opts.SpirvOptions.tShift, errors) ||

tools/clang/lib/SPIRV/SpirvEmitter.cpp

@@ -13775,6 +13775,7 @@ bool SpirvEmitter::spirvToolsOptimize(std::vector<uint32_t> *mod,
 
   spvtools::OptimizerOptions options;
   options.set_run_validator(false);
+  options.set_preserve_bindings(spirvOptions.preserveBindings);
 
   if (spirvOptions.optConfig.empty()) {
     // Add performance passes.
@@ -13815,6 +13816,7 @@ bool SpirvEmitter::spirvToolsLegalize(std::vector<uint32_t> *mod,
 
   spvtools::OptimizerOptions options;
   options.set_run_validator(false);
+  options.set_preserve_bindings(spirvOptions.preserveBindings);
   // Add interface variable SROA if the signature packing is enabled.
   if (spirvOptions.signaturePacking) {
     optimizer.RegisterPass(