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-rw-r--r--lib/CodeGen/SpillPlacement.cpp155
-rw-r--r--lib/CodeGen/SpillPlacement.h7
2 files changed, 80 insertions, 82 deletions
diff --git a/lib/CodeGen/SpillPlacement.cpp b/lib/CodeGen/SpillPlacement.cpp
index 840f05b9ff4..10a93b7fa4d 100644
--- a/lib/CodeGen/SpillPlacement.cpp
+++ b/lib/CodeGen/SpillPlacement.cpp
@@ -59,6 +59,10 @@ void SpillPlacement::getAnalysisUsage(AnalysisUsage &AU) const {
MachineFunctionPass::getAnalysisUsage(AU);
}
+/// Decision threshold. A node gets the output value 0 if the weighted sum of
+/// its inputs falls in the open interval (-Threshold;Threshold).
+static const BlockFrequency Threshold = 2;
+
/// Node - Each edge bundle corresponds to a Hopfield node.
///
/// The node contains precomputed frequency data that only depends on the CFG,
@@ -69,31 +73,25 @@ void SpillPlacement::getAnalysisUsage(AnalysisUsage &AU) const {
/// because all weights are positive.
///
struct SpillPlacement::Node {
- /// Scale - Inverse block frequency feeding into[0] or out of[1] the bundle.
- /// Ideally, these two numbers should be identical, but inaccuracies in the
- /// block frequency estimates means that we need to normalize ingoing and
- /// outgoing frequencies separately so they are commensurate.
- float Scale[2];
-
- /// Bias - Normalized contributions from non-transparent blocks.
- /// A bundle connected to a MustSpill block has a huge negative bias,
- /// otherwise it is a number in the range [-2;2].
- float Bias;
+ /// BiasN - Sum of blocks that prefer a spill.
+ BlockFrequency BiasN;
+ /// BiasP - Sum of blocks that prefer a register.
+ BlockFrequency BiasP;
/// Value - Output value of this node computed from the Bias and links.
- /// This is always in the range [-1;1]. A positive number means the variable
- /// should go in a register through this bundle.
- float Value;
+ /// This is always on of the values {-1, 0, 1}. A positive number means the
+ /// variable should go in a register through this bundle.
+ int Value;
- typedef SmallVector<std::pair<float, unsigned>, 4> LinkVector;
+ typedef SmallVector<std::pair<BlockFrequency, unsigned>, 4> LinkVector;
/// Links - (Weight, BundleNo) for all transparent blocks connecting to other
- /// bundles. The weights are all positive and add up to at most 2, weights
- /// from ingoing and outgoing nodes separately add up to a most 1. The weight
- /// sum can be less than 2 when the variable is not live into / out of some
- /// connected basic blocks.
+ /// bundles. The weights are all positive block frequencies.
LinkVector Links;
+ /// SumLinkWeights - Cached sum of the weights of all links + ThresHold.
+ BlockFrequency SumLinkWeights;
+
/// preferReg - Return true when this node prefers to be in a register.
bool preferReg() const {
// Undecided nodes (Value==0) go on the stack.
@@ -102,28 +100,24 @@ struct SpillPlacement::Node {
/// mustSpill - Return True if this node is so biased that it must spill.
bool mustSpill() const {
- // Actually, we must spill if Bias < sum(weights).
- // It may be worth it to compute the weight sum here?
- return Bias < -2.0f;
- }
-
- /// Node - Create a blank Node.
- Node() {
- Scale[0] = Scale[1] = 0;
+ // We must spill if Bias < -sum(weights) or the MustSpill flag was set.
+ // BiasN is saturated when MustSpill is set, make sure this still returns
+ // true when the RHS saturates. Note that SumLinkWeights includes Threshold.
+ return BiasN >= BiasP + SumLinkWeights;
}
/// clear - Reset per-query data, but preserve frequencies that only depend on
// the CFG.
void clear() {
- Bias = Value = 0;
+ BiasN = BiasP = Value = 0;
+ SumLinkWeights = Threshold;
Links.clear();
}
/// addLink - Add a link to bundle b with weight w.
- /// out=0 for an ingoing link, and 1 for an outgoing link.
- void addLink(unsigned b, float w, bool out) {
- // Normalize w relative to all connected blocks from that direction.
- w *= Scale[out];
+ void addLink(unsigned b, BlockFrequency w) {
+ // Update cached sum.
+ SumLinkWeights += w;
// There can be multiple links to the same bundle, add them up.
for (LinkVector::iterator I = Links.begin(), E = Links.end(); I != E; ++I)
@@ -135,33 +129,48 @@ struct SpillPlacement::Node {
Links.push_back(std::make_pair(w, b));
}
- /// addBias - Bias this node from an ingoing[0] or outgoing[1] link.
- /// Return the change to the total number of positive biases.
- void addBias(float w, bool out) {
- // Normalize w relative to all connected blocks from that direction.
- w *= Scale[out];
- Bias += w;
+ /// addBias - Bias this node.
+ void addBias(BlockFrequency freq, BorderConstraint direction) {
+ switch (direction) {
+ default:
+ break;
+ case PrefReg:
+ BiasP += freq;
+ break;
+ case PrefSpill:
+ BiasN += freq;
+ break;
+ case MustSpill:
+ BiasN = BlockFrequency::getMaxFrequency();
+ break;
+ }
}
/// update - Recompute Value from Bias and Links. Return true when node
/// preference changes.
bool update(const Node nodes[]) {
// Compute the weighted sum of inputs.
- float Sum = Bias;
- for (LinkVector::iterator I = Links.begin(), E = Links.end(); I != E; ++I)
- Sum += I->first * nodes[I->second].Value;
+ BlockFrequency SumN = BiasN;
+ BlockFrequency SumP = BiasP;
+ for (LinkVector::iterator I = Links.begin(), E = Links.end(); I != E; ++I) {
+ if (nodes[I->second].Value == -1)
+ SumN += I->first;
+ else if (nodes[I->second].Value == 1)
+ SumP += I->first;
+ }
- // The weighted sum is going to be in the range [-2;2]. Ideally, we should
- // simply set Value = sign(Sum), but we will add a dead zone around 0 for
- // two reasons:
+ // Each weighted sum is going to be less than the total frequency of the
+ // bundle. Ideally, we should simply set Value = sign(SumP - SumN), but we
+ // will add a dead zone around 0 for two reasons:
+ //
// 1. It avoids arbitrary bias when all links are 0 as is possible during
// initial iterations.
// 2. It helps tame rounding errors when the links nominally sum to 0.
- const float Thres = 1e-4f;
+ //
bool Before = preferReg();
- if (Sum < -Thres)
+ if (SumN >= SumP + Threshold)
Value = -1;
- else if (Sum > Thres)
+ else if (SumP >= SumN + Threshold)
Value = 1;
else
Value = 0;
@@ -178,23 +187,13 @@ bool SpillPlacement::runOnMachineFunction(MachineFunction &mf) {
nodes = new Node[bundles->getNumBundles()];
// Compute total ingoing and outgoing block frequencies for all bundles.
- BlockFrequency.resize(mf.getNumBlockIDs());
+ BlockFrequencies.resize(mf.getNumBlockIDs());
MachineBlockFrequencyInfo &MBFI = getAnalysis<MachineBlockFrequencyInfo>();
- float EntryFreq = BlockFrequency::getEntryFrequency();
for (MachineFunction::iterator I = mf.begin(), E = mf.end(); I != E; ++I) {
- float Freq = MBFI.getBlockFreq(I).getFrequency() / EntryFreq;
unsigned Num = I->getNumber();
- BlockFrequency[Num] = Freq;
- nodes[bundles->getBundle(Num, 1)].Scale[0] += Freq;
- nodes[bundles->getBundle(Num, 0)].Scale[1] += Freq;
+ BlockFrequencies[Num] = MBFI.getBlockFreq(I);
}
- // Scales are reciprocal frequencies.
- for (unsigned i = 0, e = bundles->getNumBundles(); i != e; ++i)
- for (unsigned d = 0; d != 2; ++d)
- if (nodes[i].Scale[d] > 0)
- nodes[i].Scale[d] = 1 / nodes[i].Scale[d];
-
// We never change the function.
return false;
}
@@ -215,12 +214,15 @@ void SpillPlacement::activate(unsigned n) {
// landing pads, or loops with many 'continue' statements. It is difficult to
// allocate registers when so many different blocks are involved.
//
- // Give a small negative bias to large bundles such that 1/32 of the
- // connected blocks need to be interested before we consider expanding the
- // region through the bundle. This helps compile time by limiting the number
- // of blocks visited and the number of links in the Hopfield network.
- if (bundles->getBlocks(n).size() > 100)
- nodes[n].Bias = -0.0625f;
+ // Give a small negative bias to large bundles such that a substantial
+ // fraction of the connected blocks need to be interested before we consider
+ // expanding the region through the bundle. This helps compile time by
+ // limiting the number of blocks visited and the number of links in the
+ // Hopfield network.
+ if (bundles->getBlocks(n).size() > 100) {
+ nodes[n].BiasP = 0;
+ nodes[n].BiasN = (BlockFrequency::getEntryFrequency() / 16);
+ }
}
@@ -229,27 +231,20 @@ void SpillPlacement::activate(unsigned n) {
void SpillPlacement::addConstraints(ArrayRef<BlockConstraint> LiveBlocks) {
for (ArrayRef<BlockConstraint>::iterator I = LiveBlocks.begin(),
E = LiveBlocks.end(); I != E; ++I) {
- float Freq = getBlockFrequency(I->Number);
- const float Bias[] = {
- 0, // DontCare,
- 1, // PrefReg,
- -1, // PrefSpill
- 0, // PrefBoth
- -HUGE_VALF // MustSpill
- };
+ BlockFrequency Freq = BlockFrequencies[I->Number];
// Live-in to block?
if (I->Entry != DontCare) {
unsigned ib = bundles->getBundle(I->Number, 0);
activate(ib);
- nodes[ib].addBias(Freq * Bias[I->Entry], 1);
+ nodes[ib].addBias(Freq, I->Entry);
}
// Live-out from block?
if (I->Exit != DontCare) {
unsigned ob = bundles->getBundle(I->Number, 1);
activate(ob);
- nodes[ob].addBias(Freq * Bias[I->Exit], 0);
+ nodes[ob].addBias(Freq, I->Exit);
}
}
}
@@ -258,15 +253,15 @@ void SpillPlacement::addConstraints(ArrayRef<BlockConstraint> LiveBlocks) {
void SpillPlacement::addPrefSpill(ArrayRef<unsigned> Blocks, bool Strong) {
for (ArrayRef<unsigned>::iterator I = Blocks.begin(), E = Blocks.end();
I != E; ++I) {
- float Freq = getBlockFrequency(*I);
+ BlockFrequency Freq = BlockFrequencies[*I];
if (Strong)
Freq += Freq;
unsigned ib = bundles->getBundle(*I, 0);
unsigned ob = bundles->getBundle(*I, 1);
activate(ib);
activate(ob);
- nodes[ib].addBias(-Freq, 1);
- nodes[ob].addBias(-Freq, 0);
+ nodes[ib].addBias(Freq, PrefSpill);
+ nodes[ob].addBias(Freq, PrefSpill);
}
}
@@ -286,9 +281,9 @@ void SpillPlacement::addLinks(ArrayRef<unsigned> Links) {
Linked.push_back(ib);
if (nodes[ob].Links.empty() && !nodes[ob].mustSpill())
Linked.push_back(ob);
- float Freq = getBlockFrequency(Number);
- nodes[ib].addLink(ob, Freq, 1);
- nodes[ob].addLink(ib, Freq, 0);
+ BlockFrequency Freq = BlockFrequencies[Number];
+ nodes[ib].addLink(ob, Freq);
+ nodes[ob].addLink(ib, Freq);
}
}
diff --git a/lib/CodeGen/SpillPlacement.h b/lib/CodeGen/SpillPlacement.h
index fc412f817cd..a0480d587d6 100644
--- a/lib/CodeGen/SpillPlacement.h
+++ b/lib/CodeGen/SpillPlacement.h
@@ -30,6 +30,7 @@
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/Support/BlockFrequency.h"
namespace llvm {
@@ -57,7 +58,7 @@ class SpillPlacement : public MachineFunctionPass {
SmallVector<unsigned, 8> RecentPositive;
// Block frequencies are computed once. Indexed by block number.
- SmallVector<float, 4> BlockFrequency;
+ SmallVector<BlockFrequency, 4> BlockFrequencies;
public:
static char ID; // Pass identification, replacement for typeid.
@@ -140,7 +141,9 @@ public:
/// getBlockFrequency - Return the estimated block execution frequency per
/// function invocation.
float getBlockFrequency(unsigned Number) const {
- return BlockFrequency[Number];
+ // FIXME: Return the BlockFrequency directly.
+ const float Scale = 1.0f / BlockFrequency::getEntryFrequency();
+ return BlockFrequencies[Number].getFrequency() * Scale;
}
private:
generated by cgit v1.2.3 (git 2.39.1) at 2024-12-20 19:50:12 +0000