[llvm] [llvm][NVPTX] Inform that 'DYNAMIC_STACKALLOC' is unsupported (PR #74684)

[Youngsuk Kim via llvm-commits]

https://github.com/JOE1994 created https://github.com/llvm/llvm-project/pull/74684

Catch unsupported path early up, and emit error with information.

Motivated by the following threads:
* https://discourse.llvm.org/t/nvptx-problems-with-dynamic-alloca/70745
* #64017

>From eee746c823e1ea216f3dc724d231fefafe9d55b8 Mon Sep 17 00:00:00 2001
From: Youngsuk Kim <youngsuk.kim at hpe.com>
Date: Wed, 6 Dec 2023 18:38:00 -0600
Subject: [PATCH] [llvm][NVPTX] Inform that 'DYNAMIC_STACKALLOC' is unsupported

Catch unsupported path early up, and emit error with information.

Motivated by the following threads:
* https://discourse.llvm.org/t/nvptx-problems-with-dynamic-alloca/70745
* #64017
---
 llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp b/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp
index 61285c6ba98df..b62072dc796e7 100644
--- a/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp
+++ b/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp
@@ -639,6 +639,11 @@ NVPTXTargetLowering::NVPTXTargetLowering(const NVPTXTargetMachine &TM,
   setOperationAction(ISD::ConstantFP, MVT::f16, Legal);
   setOperationAction(ISD::ConstantFP, MVT::bf16, Legal);
 
+  // Lowering of DYNAMIC_STACKALLOC is unsupported.
+  // Custom lower to produce an error.
+  setOperationAction(ISD::DYNAMIC_STACKALLOC, MVT::i32, Custom);
+  setOperationAction(ISD::DYNAMIC_STACKALLOC, MVT::i64, Custom);
+
   // TRAP can be lowered to PTX trap
   setOperationAction(ISD::TRAP, MVT::Other, Legal);
 
@@ -2652,6 +2657,9 @@ NVPTXTargetLowering::LowerOperation(SDValue Op, SelectionDAG &DAG) const {
   case ISD::SREM:
   case ISD::UREM:
     return LowerVectorArith(Op, DAG);
+  case ISD::DYNAMIC_STACKALLOC:
+    report_fatal_error(
+        "Dynamic stack allocation is yet unsupported by NVPTX backend.");
   default:
     llvm_unreachable("Custom lowering not defined for operation");
   }