Allow explicit data transfers to GPUs

compiler/rustc_codegen_llvm/src/back/write.rs

@@ -32,7 +32,7 @@ use crate::back::profiling::{
     LlvmSelfProfiler, selfprofile_after_pass_callback, selfprofile_before_pass_callback,
 };
 use crate::builder::SBuilder;
-use crate::builder::gpu_offload::scalar_width;
+use crate::builder::gpu_helper::scalar_width;
 use crate::common::AsCCharPtr;
 use crate::errors::{
     CopyBitcode, FromLlvmDiag, FromLlvmOptimizationDiag, LlvmError, ParseTargetMachineConfig,

compiler/rustc_codegen_llvm/src/builder.rs

@@ -4,6 +4,7 @@ use std::ops::Deref;
 
 use rustc_ast::expand::typetree::FncTree;
 pub(crate) mod autodiff;
+pub(crate) mod gpu_helper;
 pub(crate) mod gpu_offload;
 
 use libc::{c_char, c_uint};

compiler/rustc_codegen_llvm/src/builder/gpu_helper.rs

@@ -0,0 +1,178 @@
+use crate::SimpleCx;
+use crate::builder::Builder;
+use crate::llvm;
+use crate::llvm::{Type, Value};
+use rustc_abi::Align;
+use rustc_codegen_ssa::MemFlags;
+use rustc_codegen_ssa::common::TypeKind;
+use rustc_codegen_ssa::traits::{BaseTypeCodegenMethods, BuilderMethods};
+use rustc_middle::bug;
+use rustc_middle::ty::offload_meta::{OffloadMetadata, OffloadSize};
+
+pub(crate) fn scalar_width<'ll>(cx: &'ll SimpleCx<'_>, ty: &'ll Type) -> u64 {
+    match cx.type_kind(ty) {
+        TypeKind::Half
+        | TypeKind::Float
+        | TypeKind::Double
+        | TypeKind::X86_FP80
+        | TypeKind::FP128
+        | TypeKind::PPC_FP128 => cx.float_width(ty) as u64,
+        TypeKind::Integer => cx.int_width(ty),
+        other => bug!("scalar_width was called on a non scalar type {other:?}"),
+    }
+}
+
+fn get_runtime_size<'ll, 'tcx>(
+    builder: &mut Builder<'_, 'll, 'tcx>,
+    args: &[&'ll Value],
+    index: usize,
+    meta: &OffloadMetadata,
+) -> &'ll Value {
+    match meta.payload_size {
+        OffloadSize::Slice { element_size } => {
+            let length_idx = index + 1;
+            let length = args[length_idx];
+            let length_i64 = builder.intcast(length, builder.cx.type_i64(), false);
+            builder.mul(length_i64, builder.cx.get_const_i64(element_size))
+        }
+        _ => bug!("unexpected offload size {:?}", meta.payload_size),
+    }
+}
+
+// For now we have a very simplistic indexing scheme into our
+// offload_{baseptrs,ptrs,sizes}. We will probably improve this along with our gpu frontend pr.
+pub(crate) fn get_geps<'ll, 'tcx>(
+    builder: &mut Builder<'_, 'll, 'tcx>,
+    ty: &'ll Type,
+    ty2: &'ll Type,
+    a1: &'ll Value,
+    a2: &'ll Value,
+    a4: &'ll Value,
+    is_dynamic: bool,
+) -> [&'ll Value; 3] {
+    let cx = builder.cx;
+    let i32_0 = cx.get_const_i32(0);
+
+    let gep1 = builder.inbounds_gep(ty, a1, &[i32_0, i32_0]);
+    let gep2 = builder.inbounds_gep(ty, a2, &[i32_0, i32_0]);
+    let gep3 = if is_dynamic { builder.inbounds_gep(ty2, a4, &[i32_0, i32_0]) } else { a4 };
+    [gep1, gep2, gep3]
+}
+
+pub(crate) fn generate_mapper_call<'ll, 'tcx>(
+    builder: &mut Builder<'_, 'll, 'tcx>,
+    geps: [&'ll Value; 3],
+    o_type: &'ll Value,
+    fn_to_call: &'ll Value,
+    fn_ty: &'ll Type,
+    num_args: u64,
+    s_ident_t: &'ll Value,
+) {
+    let cx = builder.cx;
+    let nullptr = cx.const_null(cx.type_ptr());
+    let i64_max = cx.get_const_i64(u64::MAX);
+    let num_args = cx.get_const_i32(num_args);
+    let args =
+        vec![s_ident_t, i64_max, num_args, geps[0], geps[1], geps[2], o_type, nullptr, nullptr];
+    builder.call(fn_ty, None, None, fn_to_call, &args, None, None);
+}
+
+pub(crate) fn preper_datatransfers<'ll, 'tcx>(
+    builder: &mut Builder<'_, 'll, 'tcx>,
+    args: &[&'ll Value],
+    types: &[&Type],
+    offload_sizes: &'ll Value,
+    metadata: &[OffloadMetadata],
+    has_dynamic: bool,
+) -> (&'ll Type, &'ll Type, &'ll Value, &'ll Value, &'ll Value) {
+    let cx = builder.cx;
+    let num_args = types.len() as u64;
+    let bb = builder.llbb();
+
+    // Step 0)
+    unsafe {
+        llvm::LLVMRustPositionBuilderPastAllocas(&builder.llbuilder, builder.llfn());
+    }
+
+    let ty = cx.type_array(cx.type_ptr(), num_args);
+    // Baseptr are just the input pointer to the kernel, stored in a local alloca
+    let a1 = builder.direct_alloca(ty, Align::EIGHT, ".offload_baseptrs");
+    // Ptrs are the result of a gep into the baseptr, at least for our trivial types.
+    let a2 = builder.direct_alloca(ty, Align::EIGHT, ".offload_ptrs");
+    // These represent the sizes in bytes, e.g. the entry for `&[f64; 16]` will be 8*16.
+    let ty2 = cx.type_array(cx.type_i64(), num_args);
+
+    let a4 = if has_dynamic {
+        let alloc = builder.direct_alloca(ty2, Align::EIGHT, ".offload_sizes");
+
+        builder.memcpy(
+            alloc,
+            Align::EIGHT,
+            offload_sizes,
+            Align::EIGHT,
+            cx.get_const_i64(8 * args.len() as u64),
+            MemFlags::empty(),
+            None,
+        );
+
+        alloc
+    } else {
+        offload_sizes
+    };
+
+    // Step 1)
+    unsafe {
+        llvm::LLVMPositionBuilderAtEnd(&builder.llbuilder, bb);
+    }
+
+    // Now we allocate once per function param, a copy to be passed to one of our maps.
+    let mut vals = vec![];
+    let mut geps = vec![];
+    let i32_0 = cx.get_const_i32(0);
+    for &v in args {
+        let ty = cx.val_ty(v);
+        let ty_kind = cx.type_kind(ty);
+        let (base_val, gep_base) = match ty_kind {
+            TypeKind::Pointer => (v, v),
+            TypeKind::Half | TypeKind::Float | TypeKind::Double | TypeKind::Integer => {
+                // FIXME(Sa4dUs): check for `f128` support, latest NVIDIA cards support it
+                let num_bits = scalar_width(cx, ty);
+
+                let bb = builder.llbb();
+                unsafe {
+                    llvm::LLVMRustPositionBuilderPastAllocas(builder.llbuilder, builder.llfn());
+                }
+                let addr = builder.direct_alloca(cx.type_i64(), Align::EIGHT, "addr");
+                unsafe {
+                    llvm::LLVMPositionBuilderAtEnd(builder.llbuilder, bb);
+                }
+
+                let cast = builder.bitcast(v, cx.type_ix(num_bits));
+                let value = builder.zext(cast, cx.type_i64());
+                builder.store(value, addr, Align::EIGHT);
+                (value, addr)
+            }
+            other => bug!("offload does not support {other:?}"),
+        };
+
+        let gep = builder.inbounds_gep(cx.type_f32(), gep_base, &[i32_0]);
+
+        vals.push(base_val);
+        geps.push(gep);
+    }
+
+    for i in 0..num_args {
+        let idx = cx.get_const_i32(i);
+        let gep1 = builder.inbounds_gep(ty, a1, &[i32_0, idx]);
+        builder.store(vals[i as usize], gep1, Align::EIGHT);
+        let gep2 = builder.inbounds_gep(ty, a2, &[i32_0, idx]);
+        builder.store(geps[i as usize], gep2, Align::EIGHT);
+
+        if !matches!(metadata[i as usize].payload_size, OffloadSize::Static(_)) {
+            let gep3 = builder.inbounds_gep(ty2, a4, &[i32_0, idx]);
+            let size_val = get_runtime_size(builder, args, i as usize, &metadata[i as usize]);
+            builder.store(size_val, gep3, Align::EIGHT);
+        }
+    }
+    (ty, ty2, a1, a2, a4)
+}