AMDGPUFrameLowering.cpp revision 360784 
1//===----------------------- AMDGPUFrameLowering.cpp ----------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//==-----------------------------------------------------------------------===//
8//
9// Interface to describe a layout of a stack frame on a AMDGPU target machine.
10//
11//===----------------------------------------------------------------------===//
12
13#include "AMDGPUFrameLowering.h"
14
15using namespace llvm;
16AMDGPUFrameLowering::AMDGPUFrameLowering(StackDirection D, Align StackAl,
17                                         int LAO, Align TransAl)
18    : TargetFrameLowering(D, StackAl, LAO, TransAl) {}
19
20AMDGPUFrameLowering::~AMDGPUFrameLowering() = default;
21
22unsigned AMDGPUFrameLowering::getStackWidth(const MachineFunction &MF) const {
23  // XXX: Hardcoding to 1 for now.
24  //
25  // I think the StackWidth should stored as metadata associated with the
26  // MachineFunction.  This metadata can either be added by a frontend, or
27  // calculated by a R600 specific LLVM IR pass.
28  //
29  // The StackWidth determines how stack objects are laid out in memory.
30  // For a vector stack variable, like: int4 stack[2], the data will be stored
31  // in the following ways depending on the StackWidth.
32  //
33  // StackWidth = 1:
34  //
35  // T0.X = stack[0].x
36  // T1.X = stack[0].y
37  // T2.X = stack[0].z
38  // T3.X = stack[0].w
39  // T4.X = stack[1].x
40  // T5.X = stack[1].y
41  // T6.X = stack[1].z
42  // T7.X = stack[1].w
43  //
44  // StackWidth = 2:
45  //
46  // T0.X = stack[0].x
47  // T0.Y = stack[0].y
48  // T1.X = stack[0].z
49  // T1.Y = stack[0].w
50  // T2.X = stack[1].x
51  // T2.Y = stack[1].y
52  // T3.X = stack[1].z
53  // T3.Y = stack[1].w
54  //
55  // StackWidth = 4:
56  // T0.X = stack[0].x
57  // T0.Y = stack[0].y
58  // T0.Z = stack[0].z
59  // T0.W = stack[0].w
60  // T1.X = stack[1].x
61  // T1.Y = stack[1].y
62  // T1.Z = stack[1].z
63  // T1.W = stack[1].w
64  return 1;
65}
66