From 45461ee54e691739abfae2edc61771b359302119 Mon Sep 17 00:00:00 2001
From: Philip Rebohle <philip.rebohle@tu-dortmund.de>
Date: Tue, 24 Nov 2020 18:09:19 +0100
Subject: [PATCH] [dxbc] Use opSelect for unbound texel fetch instructions

Generates less annoying code compared to control flow instructions,
and drivers should be able to optimize away the texture instruction
anyway since the bound state is a specialization constant.
---
 src/dxbc/dxbc_compiler.cpp | 74 +++++++++++++++++++++-----------------
 src/dxbc/dxbc_compiler.h   |  7 ++++
 2 files changed, 49 insertions(+), 32 deletions(-)

diff --git a/src/dxbc/dxbc_compiler.cpp b/src/dxbc/dxbc_compiler.cpp
index 39051b1a2..6c84ee2dd 100644
--- a/src/dxbc/dxbc_compiler.cpp
+++ b/src/dxbc/dxbc_compiler.cpp
@@ -3395,15 +3395,6 @@ namespace dxvk {
     // Extract coordinates from address
     const DxbcRegisterValue coord = emitCalcTexCoord(address, imageType);
     
-    // Fetch texels only if the resource is actually bound
-    const uint32_t labelMerge     = m_module.allocateId();
-    const uint32_t labelBound     = m_module.allocateId();
-    const uint32_t labelUnbound   = m_module.allocateId();
-    
-    m_module.opSelectionMerge(labelMerge, spv::SelectionControlMaskNone);
-    m_module.opBranchConditional(m_textures.at(textureId).specId, labelBound, labelUnbound);
-    m_module.opLabel(labelBound);
-    
     // Reading a typed image or buffer view
     // always returns a four-component vector.
     const uint32_t imageId = m_module.opLoad(
@@ -3423,32 +3414,15 @@ namespace dxvk {
       ins.src[1].swizzle, ins.dst[0].mask);
     
     // If the texture is not bound, return zeroes
-    m_module.opBranch(labelMerge);
-    m_module.opLabel(labelUnbound);
-    
-    DxbcRegisterValue zeroes = [&] {
-      switch (result.type.ctype) {
-        case DxbcScalarType::Float32: return emitBuildConstVecf32(0.0f, 0.0f, 0.0f, 0.0f, ins.dst[0].mask);
-        case DxbcScalarType::Uint32:  return emitBuildConstVecu32(0u, 0u, 0u, 0u,         ins.dst[0].mask);
-        case DxbcScalarType::Sint32:  return emitBuildConstVeci32(0, 0, 0, 0,             ins.dst[0].mask);
-        default: throw DxvkError("DxbcCompiler: Invalid scalar type");
-      }
-    }();
-    
-    m_module.opBranch(labelMerge);
-    m_module.opLabel(labelMerge);
-    
-    // Merge the result with a phi function
-    const std::array<SpirvPhiLabel, 2> phiLabels = {{
-      { result.id, labelBound   },
-      { zeroes.id, labelUnbound },
-    }};
+    DxbcRegisterValue bound;
+    bound.type = { DxbcScalarType::Bool, 1 };
+    bound.id = m_textures.at(textureId).specId;
     
     DxbcRegisterValue mergedResult;
     mergedResult.type = result.type;
-    mergedResult.id = m_module.opPhi(
-      getVectorTypeId(mergedResult.type),
-      phiLabels.size(), phiLabels.data());
+    mergedResult.id = m_module.opSelect(getVectorTypeId(mergedResult.type),
+      emitBuildVector(bound, result.type.ccount).id, result.id,
+      emitBuildZeroVector(result.type).id);
     
     emitRegisterStore(ins.dst[0], mergedResult);
   }
@@ -4433,6 +4407,42 @@ namespace dxvk {
   }
   
   
+  DxbcRegisterValue DxbcCompiler::emitBuildVector(
+          DxbcRegisterValue       scalar,
+          uint32_t                count) {
+    if (count == 1)
+      return scalar;
+
+    std::array<uint32_t, 4> scalarIds =
+      { scalar.id, scalar.id, scalar.id, scalar.id };
+
+    DxbcRegisterValue result;
+    result.type.ctype = scalar.type.ctype;
+    result.type.ccount = count;
+    result.id = m_module.constComposite(
+      getVectorTypeId(result.type),
+      count, scalarIds.data());
+    return result;
+  }
+
+
+  DxbcRegisterValue DxbcCompiler::emitBuildZeroVector(
+          DxbcVectorType          type) {
+    DxbcRegisterValue result;
+    result.type.ctype = type.ctype;
+    result.type.ccount = 1;
+
+    switch (type.ctype) {
+      case DxbcScalarType::Float32: result.id = m_module.constf32(0.0f); break;
+      case DxbcScalarType::Uint32:  result.id = m_module.constu32(0u); break;
+      case DxbcScalarType::Sint32:  result.id = m_module.consti32(0); break;
+      default: throw DxvkError("DxbcCompiler: Invalid scalar type");
+    }
+
+    return emitBuildVector(result, type.ccount);
+  }
+
+
   DxbcRegisterValue DxbcCompiler::emitRegisterBitcast(
           DxbcRegisterValue       srcValue,
           DxbcScalarType          dstType) {
diff --git a/src/dxbc/dxbc_compiler.h b/src/dxbc/dxbc_compiler.h
index 55bb5ec25..90ed2a1e7 100644
--- a/src/dxbc/dxbc_compiler.h
+++ b/src/dxbc/dxbc_compiler.h
@@ -835,7 +835,14 @@ namespace dxvk {
             double                  xy,
             double                  zw,
       const DxbcRegMask&            writeMask);
+
+    DxbcRegisterValue emitBuildVector(
+            DxbcRegisterValue       scalar,
+            uint32_t                count);
     
+    DxbcRegisterValue emitBuildZeroVector(
+            DxbcVectorType          type);
+
     /////////////////////////////////////////
     // Generic register manipulation methods
     DxbcRegisterValue emitRegisterBitcast(