New approach: let the LLVM auto-upgrade mechanism take care of selecting the correct barrier intrinsic.

Author: mcourteaux

cmake/FindHalide_LLVM.cmake

@@ -40,6 +40,7 @@ if (LLVM_FOUND)
     # fallback locations.
     find_package(
         Clang
+        ${LLVM_PACKAGE_VERSION}
         HINTS
         "${LLVM_INSTALL_PREFIX}" # Same root as the LLVM we found
         "${LLVM_DIR}/../clang" # LLVM found in $ROOT/lib/cmake/llvm
@@ -51,7 +52,9 @@ if (LLVM_FOUND)
             set(Halide_LLVM_${comp}_FOUND 0)
 
             find_package(
-                LLD HINTS
+                LLD
+                ${LLVM_PACKAGE_VERSION}
+                HINTS
                 "${LLVM_INSTALL_PREFIX}"
                 # Homebrew split the LLVM and LLD packages as of version 19, so
                 # having multiple LLVM versions installed leads to the newest

src/CodeGen_PTX_Dev.cpp

@@ -262,16 +262,9 @@ 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 *barrier;
-        if ((barrier = module->getFunction("llvm.nvvm.barrier.cta.sync.aligned.all"))) {
-            // LLVM 20 and above: https://github.com/llvm/llvm-project/pull/140615
-            builder->CreateCall(barrier, builder->getInt32(0));
-        } else if ((barrier = module->getFunction("llvm.nvvm.barrier0"))) {
-            // LLVM 19: Testing for llvm.nvvm.barrier0 can be removed once we drop support for LLVM 19
-            builder->CreateCall(barrier);
-        } else {
-            internal_error << "Could not find PTX barrier intrinsic llvm.nvvm.barrier0 nor llvm.nvvm.barrier.cta.sync.aligned.all\n";
-        }
+        llvm::Function *barrier = module->getFunction("halide_ptx_barrier0");
+        internal_assert(barrier) << "Could not find PTX barrier intrinsic: halide_ptx_barrier0";
+        builder->CreateCall(barrier);
         value = ConstantInt::get(i32_t, 0);
         return;
     }

src/runtime/ptx_dev.ll

@@ -1,5 +1,3 @@
-declare void @llvm.nvvm.barrier0()
-declare void @llvm.nvvm.barrier.cta.sync.aligned.all(i32)
 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()
@@ -18,6 +16,17 @@ declare  i32 @llvm.nvvm.read.ptx.sreg.ntid.w()
 declare  i32 @llvm.nvvm.read.ptx.sreg.nctaid.w()
 declare  i32 @llvm.nvvm.read.ptx.sreg.warpsize()
 
+
+; We define our own wrapper function that calls the intrinsic above.
+; Thanks to this wrapper, it's automatically upgraded in the new LLVM to the
+; new name of the intrinsic.
+; Once we drop support for LLVM 20.1.5, we can immediately call the new intrinsic ourselves.
+declare void @llvm.nvvm.barrier0()
+define weak_odr void @halide_ptx_barrier0() nounwind uwtable readnone alwaysinline {
+       call void @llvm.nvvm.barrier0()
+       ret void
+}
+
 ; Remove these two once the minimum required llvm version is 9.0
 declare float @llvm.nvvm.atomic.load.add.f32.p0f32(float*, float)
 declare double @llvm.nvvm.atomic.load.add.f64.p0f64(double *, double)