In some rare cases, the register allocator can spill registers but end up not utilizing registers at all. The fundamental problem is linearscan's backtracking can end up freeing more than one allocated registers. However, reloads and restores might be folded into uses / defs and freed registers might not be used at all.
VirtRegMap keeps track of allocations so it knows what's not used. As a horrible hack, the stack coloring can color spill slots with *free* registers. That is, it replace reload and spills with copies from and to the free register. It unfold instructions that load and store the spill slot and replace them with register using variants.
Not yet enabled. This is part 1. More coming.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@70787 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/RegAllocLinearScan.cpp b/lib/CodeGen/RegAllocLinearScan.cpp
index 83c1cbb..b5f581c 100644
--- a/lib/CodeGen/RegAllocLinearScan.cpp
+++ b/lib/CodeGen/RegAllocLinearScan.cpp
@@ -216,6 +216,18 @@
}
void finalizeRegUses() {
+#ifndef NDEBUG
+ // Verify all the registers are "freed".
+ bool Error = false;
+ for (unsigned i = 0, e = tri_->getNumRegs(); i != e; ++i) {
+ if (regUse_[i] != 0) {
+ cerr << tri_->getName(i) << " is still in use!\n";
+ Error = true;
+ }
+ }
+ if (Error)
+ abort();
+#endif
regUse_.clear();
regUseBackUp_.clear();
}
@@ -514,6 +526,13 @@
}
DOUT << *vrm_;
+
+ // Look for physical registers that end up not being allocated even though
+ // register allocator had to spill other registers in its register class.
+ if (ls_->getNumIntervals() == 0)
+ return;
+ if (!vrm_->FindUnusedRegisters(tri_, li_))
+ return;
}
/// processActiveIntervals - expire old intervals and move non-overlapping ones
@@ -630,9 +649,9 @@
// bl should get the same spill weight otherwise it will be choosen
// as a spill candidate since spilling bh doesn't make ebx available.
for (unsigned i = 0, e = Supers.size(); i != e; ++i) {
- for (const unsigned *sr = tri_->getSubRegisters(Supers[i]); *sr; ++sr)
- if (!Processed.count(*sr))
- Weights[*sr] += weight;
+ for (const unsigned *sr = tri_->getSubRegisters(Supers[i]); *sr; ++sr)
+ if (!Processed.count(*sr))
+ Weights[*sr] += weight;
}
}
@@ -658,13 +677,14 @@
/// addStackInterval - Create a LiveInterval for stack if the specified live
/// interval has been spilled.
static void addStackInterval(LiveInterval *cur, LiveStacks *ls_,
- LiveIntervals *li_, float &Weight,
- VirtRegMap &vrm_) {
+ LiveIntervals *li_,
+ MachineRegisterInfo* mri_, VirtRegMap &vrm_) {
int SS = vrm_.getStackSlot(cur->reg);
if (SS == VirtRegMap::NO_STACK_SLOT)
return;
- LiveInterval &SI = ls_->getOrCreateInterval(SS);
- SI.weight += Weight;
+
+ const TargetRegisterClass *RC = mri_->getRegClass(cur->reg);
+ LiveInterval &SI = ls_->getOrCreateInterval(SS, RC);
VNInfo *VNI;
if (SI.hasAtLeastOneValue())
@@ -679,10 +699,10 @@
/// getConflictWeight - Return the number of conflicts between cur
/// live interval and defs and uses of Reg weighted by loop depthes.
-static float getConflictWeight(LiveInterval *cur, unsigned Reg,
- LiveIntervals *li_,
- MachineRegisterInfo *mri_,
- const MachineLoopInfo *loopInfo) {
+static
+float getConflictWeight(LiveInterval *cur, unsigned Reg, LiveIntervals *li_,
+ MachineRegisterInfo *mri_,
+ const MachineLoopInfo *loopInfo) {
float Conflicts = 0;
for (MachineRegisterInfo::reg_iterator I = mri_->reg_begin(Reg),
E = mri_->reg_end(); I != E; ++I) {
@@ -1072,12 +1092,11 @@
// linearscan.
if (cur->weight != HUGE_VALF && cur->weight <= minWeight) {
DOUT << "\t\t\tspilling(c): " << *cur << '\n';
- float SSWeight;
SmallVector<LiveInterval*, 8> spillIs;
std::vector<LiveInterval*> added =
- li_->addIntervalsForSpills(*cur, spillIs, loopInfo, *vrm_, SSWeight);
+ li_->addIntervalsForSpills(*cur, spillIs, loopInfo, *vrm_);
std::sort(added.begin(), added.end(), LISorter());
- addStackInterval(cur, ls_, li_, SSWeight, *vrm_);
+ addStackInterval(cur, ls_, li_, mri_, *vrm_);
if (added.empty())
return; // Early exit if all spills were folded.
@@ -1149,10 +1168,9 @@
spillIs.pop_back();
DOUT << "\t\t\tspilling(a): " << *sli << '\n';
earliestStart = std::min(earliestStart, sli->beginNumber());
- float SSWeight;
std::vector<LiveInterval*> newIs =
- li_->addIntervalsForSpills(*sli, spillIs, loopInfo, *vrm_, SSWeight);
- addStackInterval(sli, ls_, li_, SSWeight, *vrm_);
+ li_->addIntervalsForSpills(*sli, spillIs, loopInfo, *vrm_);
+ addStackInterval(sli, ls_, li_, mri_, *vrm_);
std::copy(newIs.begin(), newIs.end(), std::back_inserter(added));
spilled.insert(sli->reg);
}