Fix top LLVM: renamed NVPTX barrier intrinsics. (#8631)

LLVM PTX barrier intrinsics changed name: : llvm/llvm-project#141143. Now trying both, and using llvm::Function::getIntrinsicID to figure out which one is actually the working one.

Author: mcourteaux

src/CodeGen_PTX_Dev.cpp

@@ -262,9 +262,16 @@ void CodeGen_PTX_Dev::visit(const Call *op) {
         auto fence_type_ptr = as_const_int(op->args[0]);
         internal_assert(fence_type_ptr) << "gpu_thread_barrier() parameter is not a constant integer.\n";
 
-        llvm::Function *barrier0 = module->getFunction("llvm.nvvm.barrier0");
-        internal_assert(barrier0) << "Could not find PTX barrier intrinsic (llvm.nvvm.barrier0)\n";
-        builder->CreateCall(barrier0);
+        llvm::Function *barrier;
+        if ((barrier = module->getFunction("llvm.nvvm.barrier.cta.sync.aligned.all")) && barrier->getIntrinsicID() != 0) {
+            // LLVM 20.1.6 and above: https://github.com/llvm/llvm-project/pull/140615
+            builder->CreateCall(barrier, builder->getInt32(0));
+        } else if ((barrier = module->getFunction("llvm.nvvm.barrier0")) && barrier->getIntrinsicID() != 0) {
+            // LLVM 21.1.5 and below: Testing for llvm.nvvm.barrier0 can be removed once we drop support for LLVM 20
+            builder->CreateCall(barrier);
+        } else {
+            internal_error << "Could not find PTX barrier intrinsic llvm.nvvm.barrier0 nor llvm.nvvm.barrier.cta.sync.aligned.all\n";
+        }
         value = ConstantInt::get(i32_t, 0);
         return;
     }

src/runtime/ptx_dev.ll

@@ -1,4 +1,11 @@
-declare void @llvm.nvvm.barrier0()
+; The two forward declared intrinsics below refer to the same thing.
+; LLVM 20.1.6 introduced a new naming scheme for these intrinsics
+; We have to declare both, such that we can access them from the Module's
+; getFunction(), but one of those will map to an intrinsic, which we
+; will use to determine which intrinsic is supported by LLVM.
+declare void @llvm.nvvm.barrier0() ; LLVM <=20.1.5
+declare void @llvm.nvvm.barrier.cta.sync.aligned.all(i32) ; LLVM >=20.1.6
+
 declare  i32 @llvm.nvvm.read.ptx.sreg.tid.x()
 declare  i32 @llvm.nvvm.read.ptx.sreg.ctaid.x()
 declare  i32 @llvm.nvvm.read.ptx.sreg.ntid.x()