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MachineFrameInfo: Simplify pristine register calculation.

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About pristine regsiters:
Pristine registers "hold a value that is useless to the current
function, but that must be preserved - they are callee saved registers
that have not been saved." This concept saves compile time as it frees
the prologue/epilogue inserter from adding every such register to every
basic blocks live-in list.

However the current code in getPristineRegs is formulated in a
complicated way: Inside the function prologue and epilogue all callee
saves are considered pristine, while in the rest of the code only the
non-saved ones are considered pristine.  This requires logic to
differentiate between prologue/epilogue and the rest and in the presence
of shrink-wrapping this even becomes complicated/expensive.  It's also
unnecessary because the prologue epilogue inserters already mark
callee-save registers that are saved/restores properly in the respective
blocks in the prologue/epilogue (see updateLiveness() in
PrologueEpilogueInserter.cpp). So only declaring non-saved/restored
callee saved registers as pristine just works.

Differential Revision: http://reviews.llvm.org/D10101

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238524 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Matthias Braun
2015-05-28 23:20:35 +00:00
parent 7984aa9d58
commit 97c5de758a
6 changed files with 13 additions and 60 deletions
Download Patch File Download Diff File Expand all files Collapse all files

50
lib/CodeGen/MachineFunction.cpp
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@@ -584,12 +584,8 @@ int MachineFrameInfo::CreateFixedSpillStackObject(uint64_t Size,
return -++NumFixedObjects;
}
BitVector
MachineFrameInfo::getPristineRegs(const MachineBasicBlock *MBB) const {
assert(MBB && "MBB must be valid");
const MachineFunction *MF = MBB->getParent();
assert(MF && "MBB must be part of a MachineFunction");
const TargetRegisterInfo *TRI = MF->getSubtarget().getRegisterInfo();
BitVector MachineFrameInfo::getPristineRegs(const MachineFunction &MF) const {
const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
BitVector BV(TRI->getNumRegs());
// Before CSI is calculated, no registers are considered pristine. They can be
@@ -597,14 +593,10 @@ MachineFrameInfo::getPristineRegs(const MachineBasicBlock *MBB) const {
if (!isCalleeSavedInfoValid())
return BV;
for (const MCPhysReg *CSR = TRI->getCalleeSavedRegs(MF); CSR && *CSR; ++CSR)
for (const MCPhysReg *CSR = TRI->getCalleeSavedRegs(&MF); CSR && *CSR; ++CSR)
BV.set(*CSR);
// Each MBB before the save point has all CSRs pristine.
if (isBeforeSavePoint(*MF, *MBB))
return BV;
// On other MBBs the saved CSRs are not pristine.
// Saved CSRs are not pristine.
const std::vector<CalleeSavedInfo> &CSI = getCalleeSavedInfo();
for (std::vector<CalleeSavedInfo>::const_iterator I = CSI.begin(),
E = CSI.end(); I != E; ++I)
@@ -613,40 +605,6 @@ MachineFrameInfo::getPristineRegs(const MachineBasicBlock *MBB) const {
return BV;
}
// Note: We could use some sort of caching mecanism, but we lack the ability
// to know when the cache is invalid, i.e., the CFG changed.
// Assuming we have that, we can simply compute all the set of MBBs
// that are before the save point.
bool MachineFrameInfo::isBeforeSavePoint(const MachineFunction &MF,
const MachineBasicBlock &MBB) const {
// Early exit if shrink-wrapping did not kick.
if (!Save)
return &MBB == &MF.front();
// Starting from MBB, check if there is a path leading to Save that do
// not cross Restore.
SmallPtrSet<const MachineBasicBlock *, 8> Visited;
SmallVector<const MachineBasicBlock *, 8> WorkList;
WorkList.push_back(&MBB);
Visited.insert(&MBB);
do {
const MachineBasicBlock *CurBB = WorkList.pop_back_val();
// By construction, the region that is after the save point is
// dominated by the Save and post-dominated by the Restore.
// If we do not reach Restore and still reach Save, this
// means MBB is before Save.
if (CurBB == Save)
return true;
if (CurBB == Restore)
continue;
// Enqueue all the successors not already visited.
for (MachineBasicBlock *SuccBB : CurBB->successors())
if (Visited.insert(SuccBB).second)
WorkList.push_back(SuccBB);
} while (!WorkList.empty());
return false;
}
unsigned MachineFrameInfo::estimateStackSize(const MachineFunction &MF) const {
const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
const TargetRegisterInfo *RegInfo = MF.getSubtarget().getRegisterInfo();