[llvm-commits] [llvm] r132413 - /llvm/trunk/lib/CodeGen/RegAllocGreedy.cpp
Jakob Stoklund Olesen
stoklund at 2pi.dk
Wed Jun 1 11:45:02 PDT 2011
Author: stoklund
Date: Wed Jun 1 13:45:02 2011
New Revision: 132413
URL: http://llvm.org/viewvc/llvm-project?rev=132413&view=rev
Log:
Revert r132358 "Simplify the eviction policy by making the failsafe explicit."
This commit caused regressions in i386 flops-[568], matrix, salsa20,
256.bzip2, and enc-md5.
Modified:
llvm/trunk/lib/CodeGen/RegAllocGreedy.cpp
Modified: llvm/trunk/lib/CodeGen/RegAllocGreedy.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/RegAllocGreedy.cpp?rev=132413&r1=132412&r2=132413&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/RegAllocGreedy.cpp (original)
+++ llvm/trunk/lib/CodeGen/RegAllocGreedy.cpp Wed Jun 1 13:45:02 2011
@@ -39,7 +39,6 @@
#include "llvm/CodeGen/RegAllocRegistry.h"
#include "llvm/CodeGen/RegisterCoalescer.h"
#include "llvm/Target/TargetOptions.h"
-#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
@@ -53,10 +52,6 @@
STATISTIC(NumLocalSplits, "Number of split local live ranges");
STATISTIC(NumEvicted, "Number of interferences evicted");
-static cl::opt<bool>
-ComplexEviction("complex-eviction", cl::Hidden,
- cl::desc("Use complex eviction heuristics"));
-
static RegisterRegAlloc greedyRegAlloc("greedy", "greedy register allocator",
createGreedyRegisterAllocator);
@@ -99,8 +94,7 @@
enum LiveRangeStage {
RS_New, ///< Never seen before.
RS_First, ///< First time in the queue.
- RS_Evicted, ///< Requeued after being evicted.
- RS_Second, ///< Second time in the queue, ready for splitting.
+ RS_Second, ///< Second time in the queue.
RS_Global, ///< Produced by global splitting.
RS_Local, ///< Produced by local splitting.
RS_Spill ///< Produced by spilling.
@@ -124,6 +118,15 @@
}
}
+ // Eviction. Sometimes an assigned live range can be evicted without
+ // conditions, but other times it must be split after being evicted to avoid
+ // infinite loops.
+ enum CanEvict {
+ CE_Never, ///< Can never evict.
+ CE_Always, ///< Can always evict.
+ CE_WithSplit ///< Can evict only if range is also split or spilled.
+ };
+
// splitting state.
std::auto_ptr<SplitAnalysis> SA;
std::auto_ptr<SplitEditor> SE;
@@ -195,10 +198,8 @@
SlotIndex getPrevMappedIndex(const MachineInstr*);
void calcPrevSlots();
unsigned nextSplitPoint(unsigned);
- bool hasDefInRange(const LiveInterval&, const LiveInterval&);
- bool hasUseInRange(const LiveInterval&, const LiveInterval&);
- bool canEvict(LiveInterval &A, LiveInterval &B);
- bool canEvictInterference(LiveInterval&, unsigned, float&, bool);
+ CanEvict canEvict(LiveInterval &A, LiveInterval &B);
+ bool canEvictInterference(LiveInterval&, unsigned, float&);
unsigned tryAssign(LiveInterval&, AllocationOrder&,
SmallVectorImpl<LiveInterval*>&);
@@ -219,7 +220,6 @@
const char *const RAGreedy::StageName[] = {
"RS_New",
"RS_First",
- "RS_Evicted",
"RS_Second",
"RS_Global",
"RS_Local",
@@ -401,60 +401,18 @@
// Interference eviction
//===----------------------------------------------------------------------===//
-/// hasDefInRange - Returns true when any def of A happens where B is live.
-///
-/// The SSA form of live intervals guarantees:
-///
-/// A.overlaps(B) == hasDefInRange(A, B) || hasDefInRange(B, A)
-///
-bool RAGreedy::hasDefInRange(const LiveInterval &A, const LiveInterval &B) {
- for (LiveInterval::const_vni_iterator I = A.vni_begin(), E = A.vni_end();
- I != E; ++I) {
- const VNInfo *VNI = *I;
- if (VNI->isUnused())
- continue;
- if (B.liveAt(VNI->def))
- return true;
- }
- return false;
-}
-
-/// hasUseInRange - Returns true when any def or use of A happens where B is
-/// live. The following is always true:
-///
-/// A.overlaps(B) == hasUseInRange(A, B) || hasUseInRange(B, A)
-///
-bool RAGreedy::hasUseInRange(const LiveInterval &A, const LiveInterval &B) {
- if (hasDefInRange(A, B))
- return true;
- for (MachineRegisterInfo::use_nodbg_iterator I = MRI->use_nodbg_begin(A.reg),
- E = MRI->use_nodbg_end(); I != E; ++I) {
- if (I.getOperand().isUndef())
- continue;
- SlotIndex Idx = Indexes->getInstructionIndex(&*I).getDefIndex();
- if (B.liveAt(Idx))
- return true;
- }
- return false;
-}
-
/// canEvict - determine if A can evict the assigned live range B. The eviction
/// policy defined by this function together with the allocation order defined
/// by enqueue() decides which registers ultimately end up being split and
/// spilled.
///
-/// Safeguards ensure that canEvict can never cause an infinite loop.
-///
-bool RAGreedy::canEvict(LiveInterval &A, LiveInterval &B) {
- if (!ComplexEviction)
- return A.weight > B.weight;
-
- // Evict B if it has no uses in A's live range.
- if (!hasUseInRange(B, A)) {
- DEBUG(dbgs() << "Bypass: " << B << '\n');
- return true;
- }
- return A.weight > B.weight;
+/// This function must define a non-circular relation when it returns CE_Always,
+/// otherwise infinite eviction loops are possible. When evicting a <= RS_Second
+/// range, it is possible to return CE_WithSplit which forces the evicted
+/// register to be split or spilled before it can evict anything again. That
+/// guarantees progress.
+RAGreedy::CanEvict RAGreedy::canEvict(LiveInterval &A, LiveInterval &B) {
+ return A.weight > B.weight ? CE_Always : CE_Never;
}
/// canEvict - Return true if all interferences between VirtReg and PhysReg can
@@ -462,7 +420,7 @@
/// Return false if any interference is heavier than MaxWeight.
/// On return, set MaxWeight to the maximal spill weight of an interference.
bool RAGreedy::canEvictInterference(LiveInterval &VirtReg, unsigned PhysReg,
- float &MaxWeight, bool OnlyCheap) {
+ float &MaxWeight) {
float Weight = 0;
for (const unsigned *AliasI = TRI->getOverlaps(PhysReg); *AliasI; ++AliasI) {
LiveIntervalUnion::Query &Q = query(VirtReg, *AliasI);
@@ -475,22 +433,18 @@
LiveInterval *Intf = Q.interferingVRegs()[i - 1];
if (TargetRegisterInfo::isPhysicalRegister(Intf->reg))
return false;
- if (getStage(*Intf) == RS_Spill)
- return false;
if (Intf->weight >= MaxWeight)
return false;
- // When we are simply looking for a cheaper alternative, don't try too
- // hard. The evicted range shouldn't end up getting split.
- if (OnlyCheap) {
- // Don't evict something that won't be able to reevict something else.
- if (getStage(*Intf) != RS_First)
- return false;
- // Don't break a satisfied hint.
- if (VRM->getRegAllocPref(Intf->reg) == *AliasI)
+ switch (canEvict(VirtReg, *Intf)) {
+ case CE_Always:
+ break;
+ case CE_Never:
+ return false;
+ case CE_WithSplit:
+ if (getStage(*Intf) > RS_Second)
return false;
+ break;
}
- if (VirtReg.isSpillable() && !canEvict(VirtReg, *Intf))
- return false;
Weight = std::max(Weight, Intf->weight);
}
}
@@ -499,28 +453,17 @@
}
/// tryEvict - Try to evict all interferences for a physreg.
-/// @param VirtReg Currently unassigned virtual register.
-/// @param Order Physregs to try.
-/// @param CostPerUseLimit Only look at physregs below this cost per use.
-/// @return Physreg to assign VirtReg, or 0.
+/// @param VirtReg Currently unassigned virtual register.
+/// @param Order Physregs to try.
+/// @return Physreg to assign VirtReg, or 0.
unsigned RAGreedy::tryEvict(LiveInterval &VirtReg,
AllocationOrder &Order,
SmallVectorImpl<LiveInterval*> &NewVRegs,
unsigned CostPerUseLimit) {
- // Ranges that may have been evicted or requeued for splitting may never evict
- // other ranges. That could cause looping.
- // Spill ranges can always evict.
- LiveRangeStage Stage = getStage(VirtReg);
- if (Stage >= RS_Evicted && VirtReg.isSpillable())
- return 0;
NamedRegionTimer T("Evict", TimerGroupName, TimePassesIsEnabled);
- bool OnlyCheap = CostPerUseLimit != ~0u;
-
// Keep track of the lightest single interference seen so far.
- // When scavenging for a cheap register, never consider evicting heavier
- // ranges.
- float BestWeight = OnlyCheap ? VirtReg.weight : HUGE_VALF;
+ float BestWeight = HUGE_VALF;
unsigned BestPhys = 0;
Order.rewind();
@@ -532,7 +475,7 @@
continue;
float Weight = BestWeight;
- if (!canEvictInterference(VirtReg, PhysReg, Weight, OnlyCheap))
+ if (!canEvictInterference(VirtReg, PhysReg, Weight))
continue;
// This is an eviction candidate.
@@ -561,11 +504,11 @@
unassign(*Intf, VRM->getPhys(Intf->reg));
++NumEvicted;
NewVRegs.push_back(Intf);
- // Prevent looping by marking the evicted ranges as RS_Evicted.
- // When OnlyCheap is set, Intf is guaranteed to have a smaller spill
- // weight which also prevents looping.
- if (!OnlyCheap && getStage(*Intf) < RS_Evicted)
- LRStage[Intf->reg] = RS_Evicted;
+ // Prevent looping by forcing the evicted ranges to be split before they
+ // can evict anything else.
+ if (getStage(*Intf) < RS_Second &&
+ canEvict(VirtReg, *Intf) == CE_WithSplit)
+ LRStage[Intf->reg] = RS_Second;
}
}
return BestPhys;
@@ -1474,8 +1417,12 @@
LiveRangeStage Stage = getStage(VirtReg);
DEBUG(dbgs() << StageName[Stage] << '\n');
- if (unsigned PhysReg = tryEvict(VirtReg, Order, NewVRegs))
- return PhysReg;
+ // Try to evict a less worthy live range, but only for ranges from the primary
+ // queue. The RS_Second ranges already failed to do this, and they should not
+ // get a second chance until they have been split.
+ if (Stage != RS_Second)
+ if (unsigned PhysReg = tryEvict(VirtReg, Order, NewVRegs))
+ return PhysReg;
assert(NewVRegs.empty() && "Cannot append to existing NewVRegs");
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