[DirectX] Add `llvm.dx.resource.getdimensions.x` intrinsic and lowering to DXIL (#161753)

Introduces LLVM intrinsic `llvm.dx.resource.getdimensions.x` and its lowering to DXIL op `op.dx.getDimensions`.
The intrinsic will be used to implement `GetDimension` for buffers. The lowering is using `undef` value since it is required by the DXIL format which is based on LLVM 3.7.

Proposal update: https://github.com/llvm/wg-hlsl/pull/350

Closes #112982

3 files changed, 41 insertions, 0 deletions

diff --git a/llvm/lib/Target/DirectX/DXIL.td b/llvm/lib/Target/DirectX/DXIL.td
index 228114c..44c4830 100644
--- a/llvm/lib/Target/DirectX/DXIL.td
+++ b/llvm/lib/Target/DirectX/DXIL.td
@@ -57,6 +57,7 @@ def ResBindTy : DXILOpParamType;
 def ResPropsTy : DXILOpParamType;
 def SplitDoubleTy : DXILOpParamType;
 def BinaryWithCarryTy : DXILOpParamType;
+def DimensionsTy : DXILOpParamType;
 
 class DXILOpClass;
 
@@ -901,6 +902,13 @@ def CheckAccessFullyMapped : DXILOp<71, checkAccessFullyMapped> {
   let attributes = [Attributes<DXIL1_0, [ReadOnly]>];
 }
 
+def GetDimensions : DXILOp<72, getDimensions> {
+  let Doc = "gets the dimensions of a buffer or texture";
+  let arguments = [HandleTy, Int32Ty];
+  let result = DimensionsTy;
+  let stages = [Stages<DXIL1_0, [all_stages]>];
+}
+
 def Barrier : DXILOp<80, barrier> {
   let Doc = "inserts a memory barrier in the shader";
   let intrinsics = [
diff --git a/llvm/lib/Target/DirectX/DXILOpBuilder.cpp b/llvm/lib/Target/DirectX/DXILOpBuilder.cpp
index 1aed8f9..944b2e6 100644
--- a/llvm/lib/Target/DirectX/DXILOpBuilder.cpp
+++ b/llvm/lib/Target/DirectX/DXILOpBuilder.cpp
@@ -261,6 +261,12 @@ static StructType *getBinaryWithCarryType(LLVMContext &Context) {
   return StructType::create({Int32Ty, Int1Ty}, "dx.types.i32c");
 }
 
+static StructType *getDimensionsType(LLVMContext &Ctx) {
+  Type *Int32Ty = Type::getInt32Ty(Ctx);
+  return getOrCreateStructType("dx.types.Dimensions",
+                               {Int32Ty, Int32Ty, Int32Ty, Int32Ty}, Ctx);
+}
+
 static Type *getTypeFromOpParamType(OpParamType Kind, LLVMContext &Ctx,
                                     Type *OverloadTy) {
   switch (Kind) {
@@ -318,6 +324,8 @@ static Type *getTypeFromOpParamType(OpParamType Kind, LLVMContext &Ctx,
     return getSplitDoubleType(Ctx);
   case OpParamType::BinaryWithCarryTy:
     return getBinaryWithCarryType(Ctx);
+  case OpParamType::DimensionsTy:
+    return getDimensionsType(Ctx);
   }
   llvm_unreachable("Invalid parameter kind");
   return nullptr;
diff --git a/llvm/lib/Target/DirectX/DXILOpLowering.cpp b/llvm/lib/Target/DirectX/DXILOpLowering.cpp
index 610d8b6..e46a393 100644
--- a/llvm/lib/Target/DirectX/DXILOpLowering.cpp
+++ b/llvm/lib/Target/DirectX/DXILOpLowering.cpp
@@ -627,6 +627,28 @@ public:
     });
   }
 
+  [[nodiscard]] bool lowerGetDimensionsX(Function &F) {
+    IRBuilder<> &IRB = OpBuilder.getIRB();
+    Type *Int32Ty = IRB.getInt32Ty();
+
+    return replaceFunction(F, [&](CallInst *CI) -> Error {
+      IRB.SetInsertPoint(CI);
+      Value *Handle =
+          createTmpHandleCast(CI->getArgOperand(0), OpBuilder.getHandleType());
+      Value *Undef = UndefValue::get(Int32Ty);
+
+      Expected<CallInst *> OpCall = OpBuilder.tryCreateOp(
+          OpCode::GetDimensions, {Handle, Undef}, CI->getName(), Int32Ty);
+      if (Error E = OpCall.takeError())
+        return E;
+      Value *Dim = IRB.CreateExtractValue(*OpCall, 0);
+
+      CI->replaceAllUsesWith(Dim);
+      CI->eraseFromParent();
+      return Error::success();
+    });
+  }
+
   [[nodiscard]] bool lowerGetPointer(Function &F) {
     // These should have already been handled in DXILResourceAccess, so we can
     // just clean up the dead prototype.
@@ -934,6 +956,9 @@ public:
       case Intrinsic::dx_resource_updatecounter:
         HasErrors |= lowerUpdateCounter(F);
         break;
+      case Intrinsic::dx_resource_getdimensions_x:
+        HasErrors |= lowerGetDimensionsX(F);
+        break;
       case Intrinsic::ctpop:
         HasErrors |= lowerCtpopToCountBits(F);
         break;