[SPIRV] Implement Gis option for spir-v (microsoft#6840)

Fixes microsoft#3331

Author: s-perron

include/dxc/Support/SPIRVOptions.h

@@ -68,6 +68,7 @@ struct SpirvCodeGenOptions {
   bool fixFuncCallArguments;
   bool allowRWStructuredBufferArrays;
   bool enableMaximalReconvergence;
+  bool IEEEStrict;
   /// Maximum length in words for the OpString literal containing the shader
   /// source for DebugSource and DebugSourceContinued. If the source code length
   /// is larger than this number, we will use DebugSourceContinued instructions

lib/DxcSupport/HLSLOptions.cpp

@@ -327,7 +327,7 @@ static bool hasUnsupportedSpirvOption(const InputArgList &args,
   // available options and their current compatibility is needed to generate a
   // complete list.
   std::vector<OptSpecifier> unsupportedOpts = {OPT_Fd, OPT_Fre, OPT_Gec,
-                                               OPT_Gis, OPT_Qstrip_reflect};
+                                               OPT_Qstrip_reflect};
 
   for (const auto &id : unsupportedOpts) {
     if (Arg *arg = args.getLastArg(id)) {

tools/clang/lib/SPIRV/EmitVisitor.cpp

@@ -431,7 +431,8 @@ void EmitVisitor::initInstruction(SpirvInstruction *inst) {
                                spv::Decoration::RelaxedPrecision, {});
   }
   // Emit NoContraction decoration (if any).
-  if (inst->isPrecise() && inst->isArithmeticInstruction()) {
+  if ((spvOptions.IEEEStrict || inst->isPrecise()) &&
+      inst->isArithmeticInstruction()) {
     typeHandler.emitDecoration(getOrAssignResultId<SpirvInstruction>(inst),
                                spv::Decoration::NoContraction, {});
   }

tools/clang/test/CodeGenSPIRV/spirv.opt.gis.hlsl

@@ -1,5 +1,12 @@
-// RUN: not %dxc -T ps_6_0 -E main -spirv -Gis %s 2>&1 | FileCheck %s
+// RUN: %dxc -T ps_6_0 -E main -spirv -Gis %s 2>&1 | FileCheck %s
 
-void main() {}
+// Make sure the no-contraction is added for the arithmetic operation.
+// CHECK: OpDecorate [[op:%[0-9]+]] NoContraction
+
+float4 v;
+float4 main(uint col : COLOR) : SV_Target0
+{
+  // [[op]] = OpVectorTimesScalar
+  return 3*v;
+}
 
-// CHECK: -Gis is not supported with -spirv

tools/clang/tools/dxcompiler/dxcompilerobj.cpp

@@ -955,6 +955,7 @@ class DxcCompiler : public IDxcCompiler3,
         opts.SpirvOptions.codeGenHighLevel = opts.CodeGenHighLevel;
         opts.SpirvOptions.defaultRowMajor = opts.DefaultRowMajor;
         opts.SpirvOptions.disableValidation = opts.DisableValidation;
+        opts.SpirvOptions.IEEEStrict = opts.IEEEStrict;
         // Save a string representation of command line options and
         // input file name.
         if (opts.DebugInfo) {