From e2c92a311260fc80909fe75c3a47382976ba937a Mon Sep 17 00:00:00 2001 From: Jakob Stoklund Olesen Date: Fri, 16 Sep 2011 00:03:35 +0000 Subject: [PATCH] Spill mode: Hoist back-copies locally. The leaveIntvAfter() function normally inserts a back-copy after the requested instruction, making the back-copy kill the live range. In spill mode, try to insert the back-copy before the last use instead. That means the last use becomes the kill instead of the back-copy. This lowers the register pressure because the last use can now redefine the same register it was reading. This will also improve compile time: The back-copy isn't a kill, so hoisting it in hoistCopiesForSize() won't force a recomputation of the source live range. Similarly, if the back-copy isn't hoisted by the splitter, the spiller will not attempt hoisting it locally. llvm-svn: 139883 --- llvm/lib/CodeGen/SplitKit.cpp | 23 +++++++++++++++++------ 1 file changed, 17 insertions(+), 6 deletions(-) diff --git a/llvm/lib/CodeGen/SplitKit.cpp b/llvm/lib/CodeGen/SplitKit.cpp index 5f7fdccfb6a0..63627800af69 100644 --- a/llvm/lib/CodeGen/SplitKit.cpp +++ b/llvm/lib/CodeGen/SplitKit.cpp @@ -520,17 +520,28 @@ SlotIndex SplitEditor::leaveIntvAfter(SlotIndex Idx) { DEBUG(dbgs() << " leaveIntvAfter " << Idx); // The interval must be live beyond the instruction at Idx. - Idx = Idx.getBoundaryIndex(); - VNInfo *ParentVNI = Edit->getParent().getVNInfoAt(Idx); + SlotIndex Boundary = Idx.getBoundaryIndex(); + VNInfo *ParentVNI = Edit->getParent().getVNInfoAt(Boundary); if (!ParentVNI) { DEBUG(dbgs() << ": not live\n"); - return Idx.getNextSlot(); + return Boundary.getNextSlot(); } DEBUG(dbgs() << ": valno " << ParentVNI->id << '\n'); - - MachineInstr *MI = LIS.getInstructionFromIndex(Idx); + MachineInstr *MI = LIS.getInstructionFromIndex(Boundary); assert(MI && "No instruction at index"); - VNInfo *VNI = defFromParent(0, ParentVNI, Idx, *MI->getParent(), + + // In spill mode, make live ranges as short as possible by inserting the copy + // before MI. This is only possible if that instruction doesn't redefine the + // value. The inserted COPY is not a kill, and we don't need to recompute + // the source live range. The spiller also won't try to hoist this copy. + if (SpillMode && !SlotIndex::isSameInstr(ParentVNI->def, Idx) && + MI->readsVirtualRegister(Edit->getReg())) { + forceRecompute(0, ParentVNI); + defFromParent(0, ParentVNI, Idx, *MI->getParent(), MI); + return Idx; + } + + VNInfo *VNI = defFromParent(0, ParentVNI, Boundary, *MI->getParent(), llvm::next(MachineBasicBlock::iterator(MI))); return VNI->def; } -- GitLab