MachineFrameInfo: Simplify pristine register calculation.
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
llvm-svn: 238524
diff --git a/llvm/lib/CodeGen/MachineFunction.cpp b/llvm/lib/CodeGen/MachineFunction.cpp
index 8ec63f8..09662b6 100644
--- a/llvm/lib/CodeGen/MachineFunction.cpp
+++ b/llvm/lib/CodeGen/MachineFunction.cpp
@@ -584,12 +584,8 @@
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 @@
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 @@
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();