lib/Target/AMDGPU/AMDGPUFrameLowering.cpp

   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
  15 using namespace llvm;
  16 AMDGPUFrameLowering::AMDGPUFrameLowering(StackDirection D, unsigned StackAl,
  17     int LAO, unsigned TransAl)
  18   : TargetFrameLowering(D, StackAl, LAO, TransAl) { }
  19
  20 AMDGPUFrameLowering::~AMDGPUFrameLowering() = default;
  21
  22 unsigned 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 }