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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
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14
include/llvm/CodeGen/MachineFrameInfo.h
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@@ -256,11 +256,6 @@ class MachineFrameInfo {
/// Not null, if shrink-wrapping found a better place for the epilogue.
MachineBasicBlock *Restore;
/// Check if it exists a path from \p MBB leading to the basic
/// block with a SavePoint (a.k.a. prologue).
bool isBeforeSavePoint(const MachineFunction &MF,
const MachineBasicBlock &MBB) const;
public:
explicit MachineFrameInfo(unsigned StackAlign, bool isStackRealign,
bool RealignOpt)
@@ -627,16 +622,15 @@ public:
MachineBasicBlock *getRestorePoint() const { return Restore; }
void setRestorePoint(MachineBasicBlock *NewRestore) { Restore = NewRestore; }
/// getPristineRegs - Return a set of physical registers that are pristine on
/// entry to the MBB.
/// Return a set of physical registers that are pristine.
///
/// 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 yet.
/// but that must be preserved - they are callee saved registers that are not
/// saved.
///
/// Before the PrologueEpilogueInserter has placed the CSR spill code, this
/// method always returns an empty set.
BitVector getPristineRegs(const MachineBasicBlock *MBB) const;
BitVector getPristineRegs(const MachineFunction &MF) const;
/// print - Used by the MachineFunction printer to print information about
/// stack objects. Implemented in MachineFunction.cpp