Wire legalization loop unroll requirement

Author: AnastaZIuk

tools/clang/lib/SPIRV/SpirvEmitter.cpp

@@ -593,6 +593,7 @@ SpirvEmitter::SpirvEmitter(CompilerInstance &ci)
       constEvaluator(astContext, spvBuilder), entryFunction(nullptr),
       curFunction(nullptr), curThis(nullptr), seenPushConstantAt(),
       isSpecConstantMode(false), needsLegalization(false),
+      needsLegalizationLoopUnroll(false),
       beforeHlslLegalization(false), mainSourceFile(nullptr) {
 
   // Get ShaderModel from command line hlsl profile option.
@@ -5823,8 +5824,10 @@ SpirvInstruction *SpirvEmitter::createImageSample(
     SpirvInstruction *minLod, SpirvInstruction *residencyCodeId,
     SourceLocation loc, SourceRange range) {
 
-  if (varOffset)
+  if (varOffset) {
     needsLegalization = true;
+    needsLegalizationLoopUnroll = true;
+  }
 
   // SampleDref* instructions in SPIR-V always return a scalar.
   // They also have the correct type in HLSL.
@@ -16665,7 +16668,8 @@ bool SpirvEmitter::spirvToolsLegalize(std::vector<uint32_t> *mod,
     optimizer.RegisterPass(
         spvtools::CreateInterfaceVariableScalarReplacementPass());
   }
-  optimizer.RegisterLegalizationPasses(spirvOptions.preserveInterface);
+  optimizer.RegisterLegalizationPasses(spirvOptions.preserveInterface,
+                                       needsLegalizationLoopUnroll);
   // Add flattening of resources if needed.
   if (spirvOptions.flattenResourceArrays) {
     optimizer.RegisterPass(

tools/clang/lib/SPIRV/SpirvEmitter.h

@@ -1578,6 +1578,7 @@ class SpirvEmitter : public ASTConsumer {
   ///
   /// Note: legalization specific code
   bool needsLegalization;
+  bool needsLegalizationLoopUnroll;
 
   /// Whether the translated SPIR-V binary passes --before-hlsl-legalization
   /// option to spirv-val because of illegal function parameter scope.

tools/perf-repros/unroll/README.md

@@ -0,0 +1,9 @@
+This directory contains the shader payload and arguments used to investigate the SPIR-V loop unroll bottleneck on large preprocessed HLSL inputs.
+
+Use `godbolt_o5xf1hq36.hlsl` together with `godbolt_o5xf1hq36.args.txt`.
+
+Example:
+
+```text
+dxc @tools/perf-repros/unroll/godbolt_o5xf1hq36.args.txt -Fo out.spv tools/perf-repros/unroll/godbolt_o5xf1hq36.hlsl
+```

tools/perf-repros/unroll/godbolt_o5xf1hq36.args.txt

@@ -0,0 +1 @@
+-T lib_6_8  -spirv -Zpr -enable-16bit-types -fvk-use-scalar-layout -Wno-c++11-extensions -Wno-c++1z-extensions -Wno-c++14-extensions -Wno-gnu-static-float-init -fspv-target-env=vulkan1.3 -HV 202x -fspv-debug=source -fspv-debug=tool