[mlir][gpu] Introduce `host_shared` flag to `gpu.alloc`

Motivation: we have lowering pipeline based on upstream gpu and spirv dialects and and we are using host shared gpu memory to transfer data between host and device.
Add `host_shared` flag to `gpu.alloc` to distinguish between shared and device-only gpu memory allocations.

Differential Revision: https://reviews.llvm.org/D133533

mlir/include/mlir/Dialect/GPU/IR/GPUOps.td

@@ -919,15 +919,19 @@ def GPU_AllocOp : GPU_Op<"alloc", [
     it does not block until the execution has finished on the device). In
     that case, it also returns a !gpu.async.token.
 
+    If the `host_shared` keyword is present, the memory will be allocated in a
+    memory accessible both on host and on device.
+
     Example:
 
     ```mlir
-    %memref, %token = gpu.alloc async [%dep] (%width) : memref<64x?xf32, 1>
+    %memref, %token = gpu.alloc async [%dep] host_shared (%width) : memref<64x?xf32, 1>
     ```
   }];
 
   let arguments = (ins Variadic<GPU_AsyncToken>:$asyncDependencies,
-                   Variadic<Index>:$dynamicSizes, Variadic<Index>:$symbolOperands);
+                   Variadic<Index>:$dynamicSizes, Variadic<Index>:$symbolOperands,
+                   UnitAttr:$hostShared);
   let results = (outs Res<AnyMemRef, "", [MemAlloc]>:$memref,
                  Optional<GPU_AsyncToken>:$asyncToken);
 
@@ -936,7 +940,7 @@ def GPU_AllocOp : GPU_Op<"alloc", [
   }];
 
   let assemblyFormat = [{
-    custom<AsyncDependencies>(type($asyncToken), $asyncDependencies) ` `
+    custom<AsyncDependencies>(type($asyncToken), $asyncDependencies) (` ` `host_shared` $hostShared^)? ` `
     `(` $dynamicSizes `)` (`` `[` $symbolOperands^ `]`)? attr-dict `:` type($memref)
   }];
 

mlir/lib/Conversion/GPUCommon/GPUToLLVMConversion.cpp

@@ -464,6 +464,10 @@ LogicalResult ConvertHostRegisterOpToGpuRuntimeCallPattern::matchAndRewrite(
 LogicalResult ConvertAllocOpToGpuRuntimeCallPattern::matchAndRewrite(
     gpu::AllocOp allocOp, OpAdaptor adaptor,
     ConversionPatternRewriter &rewriter) const {
+  if (adaptor.getHostShared())
+    return rewriter.notifyMatchFailure(
+        allocOp, "host_shared allocation is not supported");
+
   MemRefType memRefType = allocOp.getType();
 
   if (failed(areAllLLVMTypes(allocOp, adaptor.getOperands(), rewriter)) ||

mlir/test/Dialect/GPU/ops.mlir

@@ -209,6 +209,11 @@ module attributes {gpu.container_module} {
     // CHECK: gpu.dealloc async [%[[t1]]] %[[m1]] : memref<13xf32, 1>
     %t2 = gpu.dealloc async [%t1] %m1 : memref<13xf32, 1>
 
+    // CHECK: %[[m2:.*]] = gpu.alloc host_shared () : memref<13xf32, 1>
+    %m2 = gpu.alloc host_shared () : memref<13xf32, 1>
+    // CHECK: gpu.dealloc %[[m2]] : memref<13xf32, 1>
+    gpu.dealloc %m2 : memref<13xf32, 1>
+
     return
   }