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

[Justin Bogner via llvm-commits]

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@@ -627,6 +627,30 @@ class OpLowerer {
     });
   }
 
+  [[nodiscard]] bool lowerGetDimensions(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 *Op1 = CI->getArgOperand(1);
+      if (isa<llvm::PoisonValue>(Op1))
+        Op1 = UndefValue::get(Int32Ty);
+
+      Expected<CallInst *> OpCall = OpBuilder.tryCreateOp(
+          OpCode::GetDimensions, {Handle, Op1}, CI->getName(), Int32Ty);
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bogner wrote:

There isn't really a great place to do it, but we should validate here that the results are being used correctly (That is, none of the `undef`s in the table in https://github.com/microsoft/DirectXShaderCompiler/blob/main/docs/DXIL.rst#getdimensions are being accessed) based on the type of the resource. This will prevent us from generating DXIL that wouldn't pass the validator if we're given bogus IR.

https://github.com/llvm/llvm-project/pull/161753