radeonsi/ac: move most of emit_ddxy to shared code.

We can reuse this in radv.

Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

src/amd/common/ac_llvm_util.c

@@ -851,3 +851,77 @@ ac_get_thread_id(struct ac_llvm_context *ctx)
 	set_range_metadata(ctx, tid, 0, 64);
 	return tid;
 }
+
+/*
+ * SI implements derivatives using the local data store (LDS)
+ * All writes to the LDS happen in all executing threads at
+ * the same time. TID is the Thread ID for the current
+ * thread and is a value between 0 and 63, representing
+ * the thread's position in the wavefront.
+ *
+ * For the pixel shader threads are grouped into quads of four pixels.
+ * The TIDs of the pixels of a quad are:
+ *
+ *  +------+------+
+ *  |4n + 0|4n + 1|
+ *  +------+------+
+ *  |4n + 2|4n + 3|
+ *  +------+------+
+ *
+ * So, masking the TID with 0xfffffffc yields the TID of the top left pixel
+ * of the quad, masking with 0xfffffffd yields the TID of the top pixel of
+ * the current pixel's column, and masking with 0xfffffffe yields the TID
+ * of the left pixel of the current pixel's row.
+ *
+ * Adding 1 yields the TID of the pixel to the right of the left pixel, and
+ * adding 2 yields the TID of the pixel below the top pixel.
+ */
+LLVMValueRef
+ac_emit_ddxy(struct ac_llvm_context *ctx,
+	     bool has_ds_bpermute,
+	     uint32_t mask,
+	     int idx,
+	     LLVMValueRef lds,
+	     LLVMValueRef val)
+{
+	LLVMValueRef thread_id, tl, trbl, tl_tid, trbl_tid, args[2];
+	LLVMValueRef result;
+
+	thread_id = ac_get_thread_id(ctx);
+
+	tl_tid = LLVMBuildAnd(ctx->builder, thread_id,
+			      LLVMConstInt(ctx->i32, mask, false), "");
+
+	trbl_tid = LLVMBuildAdd(ctx->builder, tl_tid,
+				LLVMConstInt(ctx->i32, idx, false), "");
+
+	if (has_ds_bpermute) {
+		args[0] = LLVMBuildMul(ctx->builder, tl_tid,
+				       LLVMConstInt(ctx->i32, 4, false), "");
+		args[1] = val;
+		tl = ac_emit_llvm_intrinsic(ctx,
+					    "llvm.amdgcn.ds.bpermute", ctx->i32,
+					    args, 2, AC_FUNC_ATTR_READNONE);
+
+		args[0] = LLVMBuildMul(ctx->builder, trbl_tid,
+				       LLVMConstInt(ctx->i32, 4, false), "");
+		trbl = ac_emit_llvm_intrinsic(ctx,
+					      "llvm.amdgcn.ds.bpermute", ctx->i32,
+					      args, 2, AC_FUNC_ATTR_READNONE);
+	} else {
+		LLVMValueRef store_ptr, load_ptr0, load_ptr1;
+
+		store_ptr = ac_build_gep0(ctx, lds, thread_id);
+		load_ptr0 = ac_build_gep0(ctx, lds, tl_tid);
+		load_ptr1 = ac_build_gep0(ctx, lds, trbl_tid);
+
+		LLVMBuildStore(ctx->builder, val, store_ptr);
+		tl = LLVMBuildLoad(ctx->builder, load_ptr0, "");
+		trbl = LLVMBuildLoad(ctx->builder, load_ptr1, "");
+	}
+
+	tl = LLVMBuildBitCast(ctx->builder, tl, ctx->f32, "");
+	trbl = LLVMBuildBitCast(ctx->builder, trbl, ctx->f32, "");
+	result = LLVMBuildFSub(ctx->builder, trbl, tl, "");
+	return result;
+}