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71 lines
2.4 KiB
C++
71 lines
2.4 KiB
C++
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//===-- MaxStackAlignment.cpp - Compute the required stack alignment -- ---===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass looks for vector register usage and aligned local objects to
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// calculate the maximum required alignment for a function. This is used by
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// targets which support it to determine if dynamic stack realignment is
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// necessary.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/CodeGen/MachineFunction.h"
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#include "llvm/CodeGen/MachineFrameInfo.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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#include "llvm/CodeGen/Passes.h"
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using namespace llvm;
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namespace {
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struct MaximalStackAlignmentCalculator : public MachineFunctionPass {
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static char ID;
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MaximalStackAlignmentCalculator() : MachineFunctionPass(&ID) {}
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virtual bool runOnMachineFunction(MachineFunction &MF) {
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MachineFrameInfo *FFI = MF.getFrameInfo();
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MachineRegisterInfo &RI = MF.getRegInfo();
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// Calculate max stack alignment of all already allocated stack objects.
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FFI->calculateMaxStackAlignment();
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unsigned MaxAlign = FFI->getMaxAlignment();
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// Be over-conservative: scan over all vreg defs and find whether vector
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// registers are used. If yes, there is probability that vector registers
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// will be spilled and thus the stack needs to be aligned properly.
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// FIXME: It would be better to only do this if a spill actually
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// happens rather than conseratively aligning the stack regardless.
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for (unsigned RegNum = TargetRegisterInfo::FirstVirtualRegister;
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RegNum < RI.getLastVirtReg(); ++RegNum)
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MaxAlign = std::max(MaxAlign, RI.getRegClass(RegNum)->getAlignment());
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if (FFI->getMaxAlignment() == MaxAlign)
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return false;
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FFI->setMaxAlignment(MaxAlign);
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return true;
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}
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virtual const char *getPassName() const {
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return "Stack Alignment Requirements Auto-Detector";
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}
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesCFG();
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MachineFunctionPass::getAnalysisUsage(AU);
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}
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};
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char MaximalStackAlignmentCalculator::ID = 0;
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}
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FunctionPass*
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llvm::createMaxStackAlignmentCalculatorPass() {
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return new MaximalStackAlignmentCalculator();
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}
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