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author | Jakob Stoklund Olesen <stoklund@2pi.dk> | 2011-04-20 18:19:48 +0000 |
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committer | Jakob Stoklund Olesen <stoklund@2pi.dk> | 2011-04-20 18:19:48 +0000 |
commit | 6bfba2e5af163442a1c6b11fe14aa9df9101cfd7 (patch) | |
tree | bfad3009de9ca920990bcde1d0b9a90e96e549be /lib/CodeGen/RegAllocGreedy.cpp | |
parent | e341e8ce1ada854e7f8fcfcf18bb2e17be2ac0ee (diff) | |
download | llvm-6bfba2e5af163442a1c6b11fe14aa9df9101cfd7.tar.gz llvm-6bfba2e5af163442a1c6b11fe14aa9df9101cfd7.tar.bz2 llvm-6bfba2e5af163442a1c6b11fe14aa9df9101cfd7.tar.xz |
Prefer cheap registers for busy live ranges.
On the x86-64 and thumb2 targets, some registers are more expensive to encode
than others in the same register class.
Add a CostPerUse field to the TableGen register description, and make it
available from TRI->getCostPerUse. This represents the cost of a REX prefix or a
32-bit instruction encoding required by choosing a high register.
Teach the greedy register allocator to prefer cheap registers for busy live
ranges (as indicated by spill weight).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129864 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/CodeGen/RegAllocGreedy.cpp')
-rw-r--r-- | lib/CodeGen/RegAllocGreedy.cpp | 50 |
1 files changed, 44 insertions, 6 deletions
diff --git a/lib/CodeGen/RegAllocGreedy.cpp b/lib/CodeGen/RegAllocGreedy.cpp index d196119711..9e58ef6d0a 100644 --- a/lib/CodeGen/RegAllocGreedy.cpp +++ b/lib/CodeGen/RegAllocGreedy.cpp @@ -187,8 +187,10 @@ private: unsigned nextSplitPoint(unsigned); bool canEvictInterference(LiveInterval&, unsigned, float&); + unsigned tryAssign(LiveInterval&, AllocationOrder&, + SmallVectorImpl<LiveInterval*>&); unsigned tryEvict(LiveInterval&, AllocationOrder&, - SmallVectorImpl<LiveInterval*>&); + SmallVectorImpl<LiveInterval*>&, unsigned = ~0u); unsigned tryRegionSplit(LiveInterval&, AllocationOrder&, SmallVectorImpl<LiveInterval*>&); unsigned tryLocalSplit(LiveInterval&, AllocationOrder&, @@ -334,6 +336,37 @@ LiveInterval *RAGreedy::dequeue() { return LI; } + +//===----------------------------------------------------------------------===// +// Direct Assignment +//===----------------------------------------------------------------------===// + +/// tryAssign - Try to assign VirtReg to an available register. +unsigned RAGreedy::tryAssign(LiveInterval &VirtReg, + AllocationOrder &Order, + SmallVectorImpl<LiveInterval*> &NewVRegs) { + Order.rewind(); + unsigned PhysReg; + while ((PhysReg = Order.next())) + if (!checkPhysRegInterference(VirtReg, PhysReg)) + break; + if (!PhysReg || Order.isHint(PhysReg)) + return PhysReg; + + // PhysReg is available. Try to evict interference from a cheaper alternative. + unsigned Cost = TRI->getCostPerUse(PhysReg); + + // Most registers have 0 additional cost. + if (!Cost) + return PhysReg; + + DEBUG(dbgs() << PrintReg(PhysReg, TRI) << " is available at cost " << Cost + << '\n'); + unsigned CheapReg = tryEvict(VirtReg, Order, NewVRegs, Cost); + return CheapReg ? CheapReg : PhysReg; +} + + //===----------------------------------------------------------------------===// // Interference eviction //===----------------------------------------------------------------------===// @@ -371,7 +404,8 @@ bool RAGreedy::canEvictInterference(LiveInterval &VirtReg, unsigned PhysReg, /// @return Physreg to assign VirtReg, or 0. unsigned RAGreedy::tryEvict(LiveInterval &VirtReg, AllocationOrder &Order, - SmallVectorImpl<LiveInterval*> &NewVRegs){ + SmallVectorImpl<LiveInterval*> &NewVRegs, + unsigned CostPerUseLimit) { NamedRegionTimer T("Evict", TimerGroupName, TimePassesIsEnabled); // Keep track of the lightest single interference seen so far. @@ -380,6 +414,12 @@ unsigned RAGreedy::tryEvict(LiveInterval &VirtReg, Order.rewind(); while (unsigned PhysReg = Order.next()) { + if (TRI->getCostPerUse(PhysReg) >= CostPerUseLimit) + continue; + // The first use of a register in a function has cost 1. + if (CostPerUseLimit == 1 && !MRI->isPhysRegUsed(PhysReg)) + continue; + float Weight = BestWeight; if (!canEvictInterference(VirtReg, PhysReg, Weight)) continue; @@ -1230,10 +1270,8 @@ unsigned RAGreedy::selectOrSplit(LiveInterval &VirtReg, SmallVectorImpl<LiveInterval*> &NewVRegs) { // First try assigning a free register. AllocationOrder Order(VirtReg.reg, *VRM, ReservedRegs); - while (unsigned PhysReg = Order.next()) { - if (!checkPhysRegInterference(VirtReg, PhysReg)) - return PhysReg; - } + if (unsigned PhysReg = tryAssign(VirtReg, Order, NewVRegs)) + return PhysReg; if (unsigned PhysReg = tryEvict(VirtReg, Order, NewVRegs)) return PhysReg; |