Temporarily revert for release (#4848)

Revert "spirv: get field index from SPIR-V type, not AST (#4806)"

This reverts commit 8f279baaef067b93199a0682aa8ec661c48be50a. This
commit isn't passing some of our internal tests and needs to be reverted
in preparation for the next Vulkan SDK release.

tools/clang/lib/SPIRV/SpirvEmitter.cpp

@@ -15,7 +15,6 @@
 
 #include "AlignmentSizeCalculator.h"
 #include "InitListHandler.h"
-#include "LowerTypeVisitor.h"
 #include "RawBufferMethods.h"
 #include "dxc/DXIL/DxilConstants.h"
 #include "dxc/HlslIntrinsicOp.h"
@@ -543,71 +542,6 @@ bool isVkRawBufferLoadIntrinsic(const clang::FunctionDecl *FD) {
   return true;
 }
 
-// Takes an AST member type, and determines its index in the equivalent SPIR-V
-// struct type. This is required as the struct layout might change between the
-// AST representation and SPIR-V representation.
-uint32_t getFieldIndexInStruct(const SpirvCodeGenOptions &spirvOptions,
-                               LowerTypeVisitor &lowerTypeVisitor,
-                               const MemberExpr *expr) {
-  // If we are accessing a derived struct, we need to account for the number
-  // of base structs, since they are placed as fields at the beginning of the
-  // derived struct.
-  auto baseType = expr->getBase()->getType();
-  if (baseType->isPointerType()) {
-    baseType = baseType->getPointeeType();
-  }
-
-  const auto *fieldDecl =
-      dynamic_cast<const FieldDecl *>(expr->getMemberDecl());
-  assert(fieldDecl);
-  const uint32_t indexAST =
-      getNumBaseClasses(baseType) + fieldDecl->getFieldIndex();
-
-  // The AST type index is not representative of the SPIR-V type index
-  // because we might squash some fields (bitfields by ex.).
-  // What we need is to match each AST node with the squashed field and then,
-  // determine the real index.
-  const SpirvType *spvType = lowerTypeVisitor.lowerType(
-      baseType, spirvOptions.sBufferLayoutRule, llvm::None, SourceLocation());
-  assert(spvType);
-
-  const auto st = dynamic_cast<const StructType *>(spvType);
-  assert(st != nullptr);
-  const auto &fields = st->getFields();
-  assert(indexAST <= fields.size());
-
-  // Some fields in SPIR-V share the same index (bitfields). Computing the final
-  // index of the requested field.
-  uint32_t indexSPV = 0;
-  for (size_t i = 1; i <= indexAST; i++) {
-    // Do not remove this condition. This is required to support inheritance:
-    // 1. SPIR-V composite first element is the parent type:
-    //  by ex "OpTypeStruct %base_struct %float".
-    // 2. if the parent type is an empty class, it's size it zero, hence
-    // "%float" offset is also 0.
-    //
-    // A way to detect such cases is to check for type difference: fields cannot
-    // be merged if the type is different.
-    if (fields[i - 1].type != fields[i].type) {
-      indexSPV++;
-      continue;
-    }
-
-    if (fields[i - 1].offset.getValueOr(0) != fields[i].offset.getValueOr(0)) {
-      indexSPV++;
-      continue;
-    }
-  }
-
-  // TODO(issue #4140): remove once bitfields are implemented.
-  // This is just a safeguard until bitfield support is in. Before bitfields,
-  // AST indices were always correct, so this function should not change that
-  // behavior. Once the bitfield support is in, indices will start to diverge,
-  // and this assert should be removed.
-  assert(indexSPV == indexAST);
-  return indexSPV;
-}
-
 } // namespace
 
 SpirvEmitter::SpirvEmitter(CompilerInstance &ci)
@@ -7680,17 +7614,23 @@ const Expr *SpirvEmitter::collectArrayStructIndices(
       }
     }
 
-    {
-      LowerTypeVisitor lowerTypeVisitor(astContext, spvContext, spirvOptions);
-      const uint32_t fieldIndex =
-          getFieldIndexInStruct(spirvOptions, lowerTypeVisitor, indexing);
-
-      if (rawIndex) {
-        rawIndices->push_back(fieldIndex);
-      } else {
-        indices->push_back(spvBuilder.getConstantInt(
-            astContext.IntTy, llvm::APInt(32, fieldIndex, true)));
-      }
+    // Append the index of the current level
+    const auto *fieldDecl = cast<FieldDecl>(indexing->getMemberDecl());
+    assert(fieldDecl);
+    // If we are accessing a derived struct, we need to account for the number
+    // of base structs, since they are placed as fields at the beginning of the
+    // derived struct.
+    auto baseType = indexing->getBase()->getType();
+    if (baseType->isPointerType()) {
+      baseType = baseType->getPointeeType();
+    }
+    const uint32_t index =
+        getNumBaseClasses(baseType) + fieldDecl->getFieldIndex();
+    if (rawIndex) {
+      rawIndices->push_back(index);
+    } else {
+      indices->push_back(spvBuilder.getConstantInt(
+          astContext.IntTy, llvm::APInt(32, index, true)));
     }
 
     return base;