[llvm] r185447 - Revert (most of) r185393 and r185395.
Jakob Stoklund Olesen
stoklund at 2pi.dk
Tue Jul 2 10:31:58 PDT 2013
Author: stoklund
Date: Tue Jul 2 12:31:58 2013
New Revision: 185447
URL: http://llvm.org/viewvc/llvm-project?rev=185447&view=rev
Log:
Revert (most of) r185393 and r185395.
"Remove floating point computations form SpillPlacement.cpp."
These commits caused test failures in lencod on clang-native-arm-lnt.
I suspect these changes are only exposing an existing issue, but
reverting anyway to keep the bots passing while we investigate.
Modified:
llvm/trunk/lib/CodeGen/SpillPlacement.cpp
llvm/trunk/lib/CodeGen/SpillPlacement.h
Modified: llvm/trunk/lib/CodeGen/SpillPlacement.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SpillPlacement.cpp?rev=185447&r1=185446&r2=185447&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SpillPlacement.cpp (original)
+++ llvm/trunk/lib/CodeGen/SpillPlacement.cpp Tue Jul 2 12:31:58 2013
@@ -59,10 +59,6 @@ void SpillPlacement::getAnalysisUsage(An
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,
@@ -73,25 +69,31 @@ static const BlockFrequency Threshold =
/// because all weights are positive.
///
struct SpillPlacement::Node {
- /// BiasN - Sum of blocks that prefer a spill.
- BlockFrequency BiasN;
- /// BiasP - Sum of blocks that prefer a register.
- BlockFrequency BiasP;
+ /// 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;
/// Value - Output value of this node computed from the Bias and links.
- /// 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;
+ /// This is always in the range [-1;1]. A positive number means the variable
+ /// should go in a register through this bundle.
+ float Value;
- typedef SmallVector<std::pair<BlockFrequency, unsigned>, 4> LinkVector;
+ typedef SmallVector<std::pair<float, unsigned>, 4> LinkVector;
/// Links - (Weight, BundleNo) for all transparent blocks connecting to other
- /// bundles. The weights are all positive block frequencies.
+ /// 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.
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.
@@ -100,24 +102,28 @@ struct SpillPlacement::Node {
/// mustSpill - Return True if this node is so biased that it must spill.
bool mustSpill() const {
- // 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;
+ // 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;
}
/// clear - Reset per-query data, but preserve frequencies that only depend on
// the CFG.
void clear() {
- BiasN = BiasP = Value = 0;
- SumLinkWeights = Threshold;
+ Bias = Value = 0;
Links.clear();
}
/// addLink - Add a link to bundle b with weight w.
- void addLink(unsigned b, BlockFrequency w) {
- // Update cached sum.
- SumLinkWeights += 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];
// There can be multiple links to the same bundle, add them up.
for (LinkVector::iterator I = Links.begin(), E = Links.end(); I != E; ++I)
@@ -129,48 +135,33 @@ struct SpillPlacement::Node {
Links.push_back(std::make_pair(w, b));
}
- /// 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;
- }
+ /// 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;
}
/// update - Recompute Value from Bias and Links. Return true when node
/// preference changes.
bool update(const Node nodes[]) {
// Compute the weighted sum of inputs.
- 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;
- }
+ float Sum = Bias;
+ for (LinkVector::iterator I = Links.begin(), E = Links.end(); I != E; ++I)
+ Sum += I->first * nodes[I->second].Value;
- // 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:
- //
+ // 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:
// 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 (SumN >= SumP + Threshold)
+ if (Sum < -Thres)
Value = -1;
- else if (SumP >= SumN + Threshold)
+ else if (Sum > Thres)
Value = 1;
else
Value = 0;
@@ -187,13 +178,23 @@ bool SpillPlacement::runOnMachineFunctio
nodes = new Node[bundles->getNumBundles()];
// Compute total ingoing and outgoing block frequencies for all bundles.
- BlockFrequencies.resize(mf.getNumBlockIDs());
+ BlockFrequency.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();
- BlockFrequencies[Num] = MBFI.getBlockFreq(I);
+ BlockFrequency[Num] = Freq;
+ nodes[bundles->getBundle(Num, 1)].Scale[0] += Freq;
+ nodes[bundles->getBundle(Num, 0)].Scale[1] += Freq;
}
+ // 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;
}
@@ -214,15 +215,12 @@ 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 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);
- }
+ // 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;
}
@@ -231,20 +229,27 @@ void SpillPlacement::activate(unsigned n
void SpillPlacement::addConstraints(ArrayRef<BlockConstraint> LiveBlocks) {
for (ArrayRef<BlockConstraint>::iterator I = LiveBlocks.begin(),
E = LiveBlocks.end(); I != E; ++I) {
- BlockFrequency Freq = BlockFrequencies[I->Number];
+ float Freq = getBlockFrequency(I->Number);
+ const float Bias[] = {
+ 0, // DontCare,
+ 1, // PrefReg,
+ -1, // PrefSpill
+ 0, // PrefBoth
+ -HUGE_VALF // MustSpill
+ };
// Live-in to block?
if (I->Entry != DontCare) {
unsigned ib = bundles->getBundle(I->Number, 0);
activate(ib);
- nodes[ib].addBias(Freq, I->Entry);
+ nodes[ib].addBias(Freq * Bias[I->Entry], 1);
}
// Live-out from block?
if (I->Exit != DontCare) {
unsigned ob = bundles->getBundle(I->Number, 1);
activate(ob);
- nodes[ob].addBias(Freq, I->Exit);
+ nodes[ob].addBias(Freq * Bias[I->Exit], 0);
}
}
}
@@ -253,15 +258,15 @@ void SpillPlacement::addConstraints(Arra
void SpillPlacement::addPrefSpill(ArrayRef<unsigned> Blocks, bool Strong) {
for (ArrayRef<unsigned>::iterator I = Blocks.begin(), E = Blocks.end();
I != E; ++I) {
- BlockFrequency Freq = BlockFrequencies[*I];
+ float Freq = getBlockFrequency(*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, PrefSpill);
- nodes[ob].addBias(Freq, PrefSpill);
+ nodes[ib].addBias(-Freq, 1);
+ nodes[ob].addBias(-Freq, 0);
}
}
@@ -281,9 +286,9 @@ void SpillPlacement::addLinks(ArrayRef<u
Linked.push_back(ib);
if (nodes[ob].Links.empty() && !nodes[ob].mustSpill())
Linked.push_back(ob);
- BlockFrequency Freq = BlockFrequencies[Number];
- nodes[ib].addLink(ob, Freq);
- nodes[ob].addLink(ib, Freq);
+ float Freq = getBlockFrequency(Number);
+ nodes[ib].addLink(ob, Freq, 1);
+ nodes[ob].addLink(ib, Freq, 0);
}
}
Modified: llvm/trunk/lib/CodeGen/SpillPlacement.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SpillPlacement.h?rev=185447&r1=185446&r2=185447&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SpillPlacement.h (original)
+++ llvm/trunk/lib/CodeGen/SpillPlacement.h Tue Jul 2 12:31:58 2013
@@ -30,7 +30,6 @@
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
-#include "llvm/Support/BlockFrequency.h"
namespace llvm {
@@ -58,7 +57,7 @@ class SpillPlacement : public MachineFu
SmallVector<unsigned, 8> RecentPositive;
// Block frequencies are computed once. Indexed by block number.
- SmallVector<BlockFrequency, 4> BlockFrequencies;
+ SmallVector<float, 4> BlockFrequency;
public:
static char ID; // Pass identification, replacement for typeid.
@@ -141,9 +140,7 @@ public:
/// getBlockFrequency - Return the estimated block execution frequency per
/// function invocation.
float getBlockFrequency(unsigned Number) const {
- // FIXME: Return the BlockFrequency directly.
- const float Scale = 1.0f / BlockFrequency::getEntryFrequency();
- return BlockFrequencies[Number].getFrequency() * Scale;
+ return BlockFrequency[Number];
}
private:
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