//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "spillplacement"
#include "SpillPlacement.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/CodeGen/EdgeBundles.h"
using namespace llvm;
+#define DEBUG_TYPE "spillplacement"
+
char SpillPlacement::ID = 0;
INITIALIZE_PASS_BEGIN(SpillPlacement, "spill-code-placement",
"Spill Code Placement Analysis", true, true)
MachineFunctionPass::getAnalysisUsage(AU);
}
+namespace {
+static BlockFrequency Threshold;
+}
+
/// 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;
+static BlockFrequency getThreshold() { return Threshold; }
+
+/// \brief Set the threshold for a given entry frequency.
+///
+/// Set the threshold relative to \c Entry. Since the threshold is used as a
+/// bound on the open interval (-Threshold;Threshold), 1 is the minimum
+/// threshold.
+static void setThreshold(const BlockFrequency &Entry) {
+ // Apparently 2 is a good threshold when Entry==2^14, but we need to scale
+ // it. Divide by 2^13, rounding as appropriate.
+ uint64_t Freq = Entry.getFrequency();
+ uint64_t Scaled = (Freq >> 13) + bool(Freq & (1 << 12));
+ Threshold = std::max(UINT64_C(1), Scaled);
+}
/// Node - Each edge bundle corresponds to a Hopfield node.
///
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.
+ /// 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<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.
// the CFG.
void clear() {
BiasN = BiasP = Value = 0;
- SumLinkWeights = Threshold;
+ SumLinkWeights = getThreshold();
Links.clear();
}
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.
+ //
bool Before = preferReg();
- if (SumN >= SumP + Threshold)
+ if (SumN >= SumP + getThreshold())
Value = -1;
- else if (SumP >= SumN + Threshold)
+ else if (SumP >= SumN + getThreshold())
Value = 1;
else
Value = 0;
// Compute total ingoing and outgoing block frequencies for all bundles.
BlockFrequencies.resize(mf.getNumBlockIDs());
- MachineBlockFrequencyInfo &MBFI = getAnalysis<MachineBlockFrequencyInfo>();
+ MBFI = &getAnalysis<MachineBlockFrequencyInfo>();
+ setThreshold(MBFI->getEntryFreq());
for (MachineFunction::iterator I = mf.begin(), E = mf.end(); I != E; ++I) {
unsigned Num = I->getNumber();
- BlockFrequencies[Num] = MBFI.getBlockFreq(I);
+ BlockFrequencies[Num] = MBFI->getBlockFreq(I);
}
// We never change the function.
void SpillPlacement::releaseMemory() {
delete[] nodes;
- nodes = 0;
+ nodes = nullptr;
}
/// activate - mark node n as active if it wasn't already.
// 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.
+ // 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);
+ nodes[n].BiasN = (MBFI->getEntryFreq() / 16);
}
}
// affect the entire network in a single iteration. That means very fast
// convergence, usually in a single iteration.
for (unsigned iteration = 0; iteration != 10; ++iteration) {
- // Scan backwards, skipping the last node which was just updated.
+ // Scan backwards, skipping the last node when iteration is not zero. When
+ // iteration is not zero, the last node was just updated.
bool Changed = false;
for (SmallVectorImpl<unsigned>::const_reverse_iterator I =
- llvm::next(Linked.rbegin()), E = Linked.rend(); I != E; ++I) {
+ iteration == 0 ? Linked.rbegin() : std::next(Linked.rbegin()),
+ E = Linked.rend(); I != E; ++I) {
unsigned n = *I;
if (nodes[n].update(nodes)) {
Changed = true;
// Scan forwards, skipping the first node which was just updated.
Changed = false;
for (SmallVectorImpl<unsigned>::const_iterator I =
- llvm::next(Linked.begin()), E = Linked.end(); I != E; ++I) {
+ std::next(Linked.begin()), E = Linked.end(); I != E; ++I) {
unsigned n = *I;
if (nodes[n].update(nodes)) {
Changed = true;
ActiveNodes->reset(n);
Perfect = false;
}
- ActiveNodes = 0;
+ ActiveNodes = nullptr;
return Perfect;
}
projects / oota-llvm.git / blobdiff