Collapse DomainValues across loop back-edges.
During the initial RPO traversal of the basic blocks, remember the ones
that are incomplete because of back-edges from predecessors that haven't
been visited yet.
After the initial RPO, revisit all those loop headers so the incoming
DomainValues on the back-edges can be properly collapsed.
This will properly fix execution domains on software pipelined code,
like the included test case.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@144151 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/ExecutionDepsFix.cpp b/lib/CodeGen/ExecutionDepsFix.cpp
index c25f7db..fc0b612 100644
--- a/lib/CodeGen/ExecutionDepsFix.cpp
+++ b/lib/CodeGen/ExecutionDepsFix.cpp
@@ -160,7 +160,7 @@
void collapse(DomainValue *dv, unsigned domain);
bool merge(DomainValue *A, DomainValue *B);
- void enterBasicBlock(MachineBasicBlock*);
+ bool enterBasicBlock(MachineBasicBlock*);
void leaveBasicBlock(MachineBasicBlock*);
void visitInstr(MachineInstr*);
void visitGenericInstr(MachineInstr*);
@@ -317,7 +317,13 @@
return true;
}
-void ExeDepsFix::enterBasicBlock(MachineBasicBlock *MBB) {
+// enterBasicBlock - Set up LiveRegs by merging predecessor live-out values.
+// Return true if some predecessor hasn't been processed yet (like on a loop
+// back-edge).
+bool ExeDepsFix::enterBasicBlock(MachineBasicBlock *MBB) {
+ // Detect back-edges from predecessors we haven't processed yet.
+ bool seenBackEdge = false;
+
// Try to coalesce live-out registers from predecessors.
for (MachineBasicBlock::livein_iterator i = MBB->livein_begin(),
e = MBB->livein_end(); i != e; ++i) {
@@ -326,7 +332,12 @@
for (MachineBasicBlock::const_pred_iterator pi = MBB->pred_begin(),
pe = MBB->pred_end(); pi != pe; ++pi) {
LiveOutMap::const_iterator fi = LiveOuts.find(*pi);
- if (fi == LiveOuts.end()) continue;
+ if (fi == LiveOuts.end()) {
+ seenBackEdge = true;
+ continue;
+ }
+ if (!fi->second)
+ continue;
DomainValue *pdv = resolve(fi->second[rx]);
if (!pdv) continue;
if (!LiveRegs || !LiveRegs[rx]) {
@@ -350,12 +361,19 @@
force(rx, pdv->getFirstDomain());
}
}
+ return seenBackEdge;
}
void ExeDepsFix::leaveBasicBlock(MachineBasicBlock *MBB) {
// Save live registers at end of MBB - used by enterBasicBlock().
- if (LiveRegs)
- LiveOuts.insert(std::make_pair(MBB, LiveRegs));
+ // Also use LiveOuts as a visited set to detect back-edges.
+ if (!LiveOuts.insert(std::make_pair(MBB, LiveRegs)).second && LiveRegs) {
+ // Insertion failed, this must be the second pass.
+ // Release all the DomainValues instead of keeping them.
+ for (unsigned i = 0, e = NumRegs; i != e; ++i)
+ release(LiveRegs[i]);
+ delete[] LiveRegs;
+ }
LiveRegs = 0;
}
@@ -545,23 +563,32 @@
MachineBasicBlock *Entry = MF->begin();
ReversePostOrderTraversal<MachineBasicBlock*> RPOT(Entry);
+ SmallVector<MachineBasicBlock*, 16> Loops;
for (ReversePostOrderTraversal<MachineBasicBlock*>::rpo_iterator
MBBI = RPOT.begin(), MBBE = RPOT.end(); MBBI != MBBE; ++MBBI) {
MachineBasicBlock *MBB = *MBBI;
- enterBasicBlock(MBB);
+ if (enterBasicBlock(MBB))
+ Loops.push_back(MBB);
for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E;
++I)
visitInstr(I);
leaveBasicBlock(MBB);
}
+ // Visit all the loop blocks again in order to merge DomainValues from
+ // back-edges.
+ for (unsigned i = 0, e = Loops.size(); i != e; ++i) {
+ MachineBasicBlock *MBB = Loops[i];
+ enterBasicBlock(MBB);
+ leaveBasicBlock(MBB);
+ }
+
// Clear the LiveOuts vectors and collapse any remaining DomainValues.
for (ReversePostOrderTraversal<MachineBasicBlock*>::rpo_iterator
MBBI = RPOT.begin(), MBBE = RPOT.end(); MBBI != MBBE; ++MBBI) {
LiveOutMap::const_iterator FI = LiveOuts.find(*MBBI);
- if (FI == LiveOuts.end())
+ if (FI == LiveOuts.end() || !FI->second)
continue;
- assert(FI->second && "Null entry");
for (unsigned i = 0, e = NumRegs; i != e; ++i)
if (FI->second[i])
release(FI->second[i]);