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llvm-mirror/lib/Target/Sparc/SparcRegisterInfo.h
James Y Knight af99ad073e [Sparc] Support user-specified stack object overalignment.
Note: I do not implement a base pointer, so it's still impossible to
have dynamic realignment AND dynamic alloca in the same function.

This also moves the code for determining the frame index reference
into getFrameIndexReference, where it belongs, instead of inline in
eliminateFrameIndex.

[Begin long-winded screed]

Now, stack realignment for Sparc is actually a silly thing to support,
because the Sparc ABI has no need for it -- unlike the situation on
x86, the stack is ALWAYS aligned to the required alignment for the CPU
instructions: 8 bytes on sparcv8, and 16 bytes on sparcv9.

However, LLVM unfortunately implements user-specified overalignment
using stack realignment support, so for now, I'm going to go along
with that tradition. GCC instead treats objects which have alignment
specification greater than the maximum CPU-required alignment for the
target as a separate block of stack memory, with their own virtual
base pointer (which gets aligned). Doing it that way avoids needing to
implement per-target support for stack realignment, except for the
targets which *actually* have an ABI-specified stack alignment which
is too small for the CPU's requirements.

Further unfortunately in LLVM, the default canRealignStack for all
targets effectively returns true, despite that implementing that is
something a target needs to do specifically. So, the previous behavior
on Sparc was to silently ignore the user's specified stack
alignment. Ugh.

Yet MORE unfortunate, if a target actually does return false from
canRealignStack, that also causes the user-specified alignment to be
*silently ignored*, rather than emitting an error.

(I started looking into fixing that last, but it broke a bunch of
tests, because LLVM actually *depends* on having it silently ignored:
some architectures (e.g. non-linux i386) have smaller stack alignment
than spilled-register alignment. But, the fact that a register needs
spilling is not known until within the register allocator. And by that
point, the decision to not reserve the frame pointer has been frozen
in place. And without a frame pointer, stack realignment is not
possible. So, canRealignStack() returns false, and
needsStackRealignment() then returns false, assuming everyone can just
go on their merry way assuming the alignment requirements were
probably just suggestions after-all. Sigh...)

Differential Revision: http://reviews.llvm.org/D12208

llvm-svn: 245668
2015-08-21 04:17:56 +00:00

54 lines
1.8 KiB
C++

//===-- SparcRegisterInfo.h - Sparc Register Information Impl ---*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains the Sparc implementation of the TargetRegisterInfo class.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_LIB_TARGET_SPARC_SPARCREGISTERINFO_H
#define LLVM_LIB_TARGET_SPARC_SPARCREGISTERINFO_H
#include "llvm/Target/TargetRegisterInfo.h"
#define GET_REGINFO_HEADER
#include "SparcGenRegisterInfo.inc"
namespace llvm {
struct SparcRegisterInfo : public SparcGenRegisterInfo {
SparcRegisterInfo();
/// Code Generation virtual methods...
const MCPhysReg *getCalleeSavedRegs(const MachineFunction *MF) const override;
const uint32_t *getCallPreservedMask(const MachineFunction &MF,
CallingConv::ID CC) const override;
const uint32_t* getRTCallPreservedMask(CallingConv::ID CC) const;
BitVector getReservedRegs(const MachineFunction &MF) const override;
const TargetRegisterClass *getPointerRegClass(const MachineFunction &MF,
unsigned Kind) const override;
void eliminateFrameIndex(MachineBasicBlock::iterator II,
int SPAdj, unsigned FIOperandNum,
RegScavenger *RS = nullptr) const override;
void processFunctionBeforeFrameFinalized(MachineFunction &MF,
RegScavenger *RS = nullptr) const;
unsigned getFrameRegister(const MachineFunction &MF) const override;
bool canRealignStack(const MachineFunction &MF) const override;
};
} // end namespace llvm
#endif