[flang-commits] [flang] [flang][cuda] Fix GPULaunchKernelConversion to generate correct kernel launch parameters (PR #119431)

[via flang-commits]

https://github.com/khaki3 created https://github.com/llvm/llvm-project/pull/119431

For the call to _FortranACUFLaunchKernel, we store the pointer to a member of a temporary structure in a parameter array. However, when we obtain an element pointer from the parameter array, its address is calculated based on the type of the structure. This PR properly treats the parameter array as an array of pointers.

Example:

```mlir
%30 = llvm.load %29 : !llvm.ptr -> i32
%31 = llvm.mlir.constant(1 : i32) : i32
%32 = llvm.alloca %31 x !llvm.struct<(i64, i64, i32, ptr)> : (i32) -> !llvm.ptr
%33 = llvm.mlir.constant(4 : i32) : i32
%34 = llvm.alloca %33 x !llvm.ptr : (i32) -> !llvm.ptr
%35 = llvm.mlir.constant(0 : i32) : i32
%36 = llvm.getelementptr %32[%35] : (!llvm.ptr, i32) -> !llvm.ptr, !llvm.struct<(i64, i64, i32, ptr)>
llvm.store %8, %36 : i64, !llvm.ptr
%37 = llvm.getelementptr %34[%35] : (!llvm.ptr, i32) -> !llvm.ptr, !llvm.struct<(i64, i64, i32, ptr)>
llvm.store %36, %37 : !llvm.ptr, !llvm.ptr
...
llvm.call @_FortranACUFLaunchKernel(%47, %8, %8, %8, %2, %8, %8, %7, %34, %48) : (!llvm.ptr, i64, i64, i64, i64, i64, i64, i32, !llvm.ptr, !llvm.ptr) -> () 
```
In this example, `%37 = llvm.getelementptr %34[%35] : (!llvm.ptr, i32) -> !llvm.ptr, !llvm.struct<(i64, i64, i32, ptr)>` will be `%37 = llvm.getelementptr %34[%35] : (!llvm.ptr, i32) -> !llvm.ptr, !llvm.ptr`.


>From 00a2350a670e37d9feb0779ff9d0b97ce3e1d789 Mon Sep 17 00:00:00 2001
From: Kazuaki Matsumura <kmatsumura at nvidia.com>
Date: Tue, 10 Dec 2024 10:44:29 -0800
Subject: [PATCH] [flang][cuda] Fix GPULaunchKernelConversion to generate
 correct kernel launch parameters

---
 .../Optimizer/Transforms/CUFGPUToLLVMConversion.cpp   |  2 +-
 flang/test/Fir/CUDA/cuda-gpu-launch-func.mlir         | 11 +++++++++--
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/flang/lib/Optimizer/Transforms/CUFGPUToLLVMConversion.cpp b/flang/lib/Optimizer/Transforms/CUFGPUToLLVMConversion.cpp
index c64f35542a6e59..426cd52b7ef83e 100644
--- a/flang/lib/Optimizer/Transforms/CUFGPUToLLVMConversion.cpp
+++ b/flang/lib/Optimizer/Transforms/CUFGPUToLLVMConversion.cpp
@@ -58,7 +58,7 @@ static mlir::Value createKernelArgArray(mlir::Location loc,
         loc, ptrTy, structTy, argStruct, mlir::ArrayRef<mlir::Value>({indice}));
     rewriter.create<LLVM::StoreOp>(loc, arg, structMember);
     mlir::Value arrayMember = rewriter.create<LLVM::GEPOp>(
-        loc, ptrTy, structTy, argArray, mlir::ArrayRef<mlir::Value>({indice}));
+        loc, ptrTy, ptrTy, argArray, mlir::ArrayRef<mlir::Value>({indice}));
     rewriter.create<LLVM::StoreOp>(loc, structMember, arrayMember);
   }
   return argArray;
diff --git a/flang/test/Fir/CUDA/cuda-gpu-launch-func.mlir b/flang/test/Fir/CUDA/cuda-gpu-launch-func.mlir
index 7fede7c6c17b78..accdeae30aa61c 100644
--- a/flang/test/Fir/CUDA/cuda-gpu-launch-func.mlir
+++ b/flang/test/Fir/CUDA/cuda-gpu-launch-func.mlir
@@ -99,9 +99,16 @@ module attributes {dlti.dl_spec = #dlti.dl_spec<#dlti.dl_entry<i1, dense<8> : ve
 }
 
 // CHECK-LABEL: _QMmod1Phost_sub
-
+// CHECK: %[[STRUCT:.*]] = llvm.alloca %{{.*}} x !llvm.struct<(ptr)> : (i32) -> !llvm.ptr
+// CHECK: %[[PARAMS:.*]] = llvm.alloca %{{.*}} x !llvm.ptr : (i32) -> !llvm.ptr
+// CHECK: %[[ZERO:.*]] = llvm.mlir.constant(0 : i32) : i32
+// CHECK: %[[STRUCT_PTR:.*]] = llvm.getelementptr %[[STRUCT]][%[[ZERO]]] : (!llvm.ptr, i32) -> !llvm.ptr, !llvm.struct<(ptr)>
+// CHECK: llvm.store %{{.*}}, %[[STRUCT_PTR]] : !llvm.ptr, !llvm.ptr
+// CHECK: %[[PARAM_PTR:.*]] = llvm.getelementptr %[[PARAMS]][%[[ZERO]]] : (!llvm.ptr, i32) -> !llvm.ptr, !llvm.ptr
+// CHECK: llvm.store %[[STRUCT_PTR]], %[[PARAM_PTR]] : !llvm.ptr, !llvm.ptr
 // CHECK: %[[KERNEL_PTR:.*]] = llvm.mlir.addressof @_QMmod1Psub1 : !llvm.ptr
-// CHECK: llvm.call @_FortranACUFLaunchKernel(%[[KERNEL_PTR]], {{.*}})
+// CHECK: %[[NULL:.*]] = llvm.mlir.zero : !llvm.ptr
+// CHECK: llvm.call @_FortranACUFLaunchKernel(%[[KERNEL_PTR]], {{.*}}, %[[PARAMS]], %[[NULL]])
 
 // -----