[dxbc] Add option to enable strict sm4-compliat division

SM4 is defined to return the first source operand if the divisor is zero.
Windows drivers don't do this by default, so we shouldn't do it either.

src/d3d11/d3d11_options.cpp

@@ -7,6 +7,7 @@ namespace dxvk {
   D3D11Options::D3D11Options(const Config& config) {
     this->allowMapFlagNoWait    = config.getOption<bool>("d3d11.allowMapFlagNoWait", false);
     this->dcSingleUseMode       = config.getOption<bool>("d3d11.dcSingleUseMode", true);
+    this->strictDivision          = config.getOption<bool>("d3d11.strictDivision", false);
     this->zeroInitWorkgroupMemory = config.getOption<bool>("d3d11.zeroInitWorkgroupMemory", false);
     this->maxTessFactor         = config.getOption<int32_t>("d3d11.maxTessFactor", 0);
     this->samplerAnisotropy     = config.getOption<int32_t>("d3d11.samplerAnisotropy", -1);

src/d3d11/d3d11_options.h

@@ -25,6 +25,11 @@ namespace dxvk {
     /// than once.
     bool dcSingleUseMode;
 
+    /// Enables sm4-compliant division-by-zero behaviour
+    /// Windows drivers don't normally do this, but some
+    /// games may expect correct behaviour.
+    bool strictDivision;
+
     /// Zero-initialize workgroup memory
     ///
     /// Workargound for games that don't initialize

src/dxbc/dxbc_compiler.cpp

@@ -1519,6 +1519,21 @@ namespace dxvk {
         break;
         
       case DxbcOpcode::Div:
+        dst.id = m_module.opFDiv(typeId,
+          src.at(0).id, src.at(1).id);
+        
+        if (m_moduleInfo.options.strictDivision) {
+          uint32_t boolType = dst.type.ccount > 1
+            ? m_module.defVectorType(m_module.defBoolType(), dst.type.ccount)
+            : m_module.defBoolType();
+          
+          dst.id = m_module.opSelect(typeId,
+            m_module.opFOrdNotEqual(boolType, src.at(1).id,
+              emitBuildConstVecf32(0.0f, 0.0f, 0.0f, 0.0f, ins.dst[0].mask).id),
+            dst.id, src.at(0).id);
+        }
+        break;
+
       case DxbcOpcode::DDiv:
         dst.id = m_module.opFDiv(typeId,
           src.at(0).id, src.at(1).id);

src/dxbc/dxbc_options.cpp

@@ -24,6 +24,7 @@ namespace dxvk {
     useRawSsbo
       = (devInfo.core.properties.limits.minStorageBufferOffsetAlignment <= sizeof(uint32_t));
     
+    strictDivision          = options.strictDivision;
     zeroInitWorkgroupMemory = options.zeroInitWorkgroupMemory;
     
     // Disable early discard on RADV due to GPU hangs

src/dxbc/dxbc_options.h

@@ -21,6 +21,9 @@ namespace dxvk {
     /// for raw and structured buffers.
     bool useRawSsbo = false;
 
+    /// Enables sm4-compliant division-by-zero behaviour
+    bool strictDivision = false;
+
     /// Clear thread-group shared memory to zero
     bool zeroInitWorkgroupMemory = false;
   };