[llvm-branch-commits] [clang] [HLSL] Global resource arrays element access (PR #152454)

[Joshua Batista via llvm-branch-commits]

================
@@ -701,3 +808,95 @@ void CGHLSLRuntime::emitInitListOpaqueValues(CodeGenFunction &CGF,
     }
   }
 }
+
+std::optional<LValue> CGHLSLRuntime::emitResourceArraySubscriptExpr(
+    const ArraySubscriptExpr *ArraySubsExpr, CodeGenFunction &CGF) {
+  assert(ArraySubsExpr->getType()->isHLSLResourceRecord() ||
+         ArraySubsExpr->getType()->isHLSLResourceRecordArray() &&
+             "expected resource array subscript expression");
+
+  // let clang codegen handle local resource array subscrips
+  const VarDecl *ArrayDecl = dyn_cast<VarDecl>(getArrayDecl(ArraySubsExpr));
+  if (!ArrayDecl || !ArrayDecl->hasGlobalStorage())
+    return std::nullopt;
+
+  // FIXME: this is not yet implemented (llvm/llvm-project#145426)
+  assert(!ArraySubsExpr->getType()->isArrayType() &&
+         "indexing of array subsets it not supported yet");
+
+  // get total array size (= range size)
+  const Type *ResArrayTy = ArrayDecl->getType().getTypePtr();
+  assert(ResArrayTy->isHLSLResourceRecordArray() &&
+         "expected array of resource classes");
+  llvm::Value *Range =
+      llvm::ConstantInt::get(CGM.IntTy, getTotalArraySize(ResArrayTy));
+
+  // Iterate through all nested array subscript expressions to calculate
+  // the index in the flattened resource array (if this is a multi-
+  // dimensional array). The index is calculated as a sum of all indices
+  // multiplied by the total size of the array at that level.
+  Value *Index = nullptr;
+  Value *Multiplier = nullptr;
+  const ArraySubscriptExpr *ASE = ArraySubsExpr;
+  while (ASE != nullptr) {
+    Value *SubIndex = CGF.EmitScalarExpr(ASE->getIdx());
----------------
bob80905 wrote:

Just curious: why is it that we need to create instructions to dynamically compute this? Wouldn't we be able to use an int, find the value, and then create the value at the end right before Index's use at 891?

https://github.com/llvm/llvm-project/pull/152454