6502/llvm-6502
1
0
Fork 0
mirror of https://github.com/c64scene-ar/llvm-6502.git synced 2026-04-24 13:18:17 +00:00
Code Issues Projects Releases Wiki Activity

RegAlloc: Account for a variable entry block frequency

Browse Source 
Until r197284, the entry frequency was constant -- i.e., set to 2^14.
Although current ToT still has a constant entry frequency, since r197284
that has been an implementation detail (which is soon going to change).

  - r204690 made the wrong assumption for the CSRCost metric.  Adjust
    callee-saved register cost based on entry frequency.

  - r185393 made the wrong assumption (although it was valid at the
    time).  Update SpillPlacement.cpp::Threshold to be relative to the
    entry frequency.

Since ToT still has 2^14 entry frequency, this should have no observable
functionality change.

<rdar://problem/14292693>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205789 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan P. N. Exon Smith
2014-04-08 19:18:56 +00:00
parent c0c10f20a2
commit 861e4db905
2 changed files with 58 additions and 13 deletions
Download Patch File Download Diff File Expand all files Collapse all files
lib/CodeGen/SpillPlacement.cpp
+22 -4
View File
@@ -59,9 +59,26 @@ void SpillPlacement::getAnalysisUsage(AnalysisUsage &AU) const {
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.
///
@@ -110,7 +127,7 @@ struct SpillPlacement::Node {
// the CFG.
void clear() {
BiasN = BiasP = Value = 0;
SumLinkWeights = Threshold;
SumLinkWeights = getThreshold();
Links.clear();
}
@@ -168,9 +185,9 @@ struct SpillPlacement::Node {
// 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;
@@ -189,6 +206,7 @@ bool SpillPlacement::runOnMachineFunction(MachineFunction &mf) {
// Compute total ingoing and outgoing block frequencies for all bundles.
BlockFrequencies.resize(mf.getNumBlockIDs());
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);