Add SplitEditor::overlapIntv() to create small ranges where both registers are live.
If a live range is used by a terminator instruction, and that live range needs
to leave the block on the stack or in a different register, it can be necessary
to have both sides of the split live at the terminator instruction.
Example:
%vreg2 = COPY %vreg1
JMP %vreg1
Becomes after spilling %vreg2:
SPILL %vreg1
JMP %vreg1
The spill doesn't kill the register as is normally the case.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@125102 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/RegAllocGreedy.cpp b/lib/CodeGen/RegAllocGreedy.cpp
index ff0c790..be01bdc 100644
--- a/lib/CodeGen/RegAllocGreedy.cpp
+++ b/lib/CodeGen/RegAllocGreedy.cpp
@@ -746,6 +746,7 @@
assert(Use <= BI.LastUse && "Couldn't find last use");
SlotIndex SegStart = SE.enterIntvBefore(Use);
assert(SegStart >= IP.second && "Couldn't avoid interference");
+ assert(SegStart < BI.LastSplitPoint && "Impossible split point");
SE.useIntv(SegStart, Stop);
continue;
}
@@ -798,8 +799,30 @@
if (!RegOut) {
// Block is live-through, but exit bundle is on the stack.
// Spill immediately after the last use.
- DEBUG(dbgs() << ", uses, stack-out.\n");
- SE.useIntv(Start, SE.leaveIntvAfter(BI.LastUse));
+ if (BI.LastUse < BI.LastSplitPoint) {
+ DEBUG(dbgs() << ", uses, stack-out.\n");
+ SE.useIntv(Start, SE.leaveIntvAfter(BI.LastUse));
+ continue;
+ }
+ // The last use is after the last split point, it is probably an
+ // indirect jump.
+ DEBUG(dbgs() << ", uses at " << BI.LastUse << " after split point "
+ << BI.LastSplitPoint << ", stack-out.\n");
+ SlotIndex SegEnd;
+ if (BI.LastSplitPoint == Start)
+ SegEnd = SE.leaveIntvAtTop(*BI.MBB);
+ else {
+ MachineBasicBlock::iterator I =
+ LIS->getInstructionFromIndex(BI.LastSplitPoint);
+ do assert(I != BI.MBB->begin() && "Expected instruction");
+ while ((--I)->isDebugValue());
+ SegEnd = SE.leaveIntvAfter(LIS->getInstructionIndex(I));
+ }
+ SE.useIntv(Start, SegEnd);
+ // Run a double interval from the split to the last use.
+ // This makes it possible to spill the complement without affecting the
+ // indirect branch.
+ SE.overlapIntv(SegEnd, BI.LastUse);
continue;
}
// Register is live-through.
diff --git a/lib/CodeGen/SplitKit.cpp b/lib/CodeGen/SplitKit.cpp
index 0c2a2cf..e26d909 100644
--- a/lib/CodeGen/SplitKit.cpp
+++ b/lib/CodeGen/SplitKit.cpp
@@ -882,6 +882,22 @@
return VNI->def;
}
+void SplitEditor::overlapIntv(SlotIndex Start, SlotIndex End) {
+ assert(OpenIdx && "openIntv not called before overlapIntv");
+ assert(Edit.getParent().getVNInfoAt(Start) ==
+ Edit.getParent().getVNInfoAt(End.getPrevSlot()) &&
+ "Parent changes value in extended range");
+ assert(Edit.get(0)->getVNInfoAt(Start) && "Start must come from leaveIntv*");
+ assert(LIS.getMBBFromIndex(Start) == LIS.getMBBFromIndex(End) &&
+ "Range cannot span basic blocks");
+
+ // Treat this as useIntv() for now. The complement interval will be extended
+ // as needed by mapValue().
+ DEBUG(dbgs() << " overlapIntv [" << Start << ';' << End << "):");
+ RegAssign.insert(Start, End, OpenIdx);
+ DEBUG(dump());
+}
+
/// closeIntv - Indicate that we are done editing the currently open
/// LiveInterval, and ranges can be trimmed.
void SplitEditor::closeIntv() {
diff --git a/lib/CodeGen/SplitKit.h b/lib/CodeGen/SplitKit.h
index 205341c..4614796 100644
--- a/lib/CodeGen/SplitKit.h
+++ b/lib/CodeGen/SplitKit.h
@@ -377,6 +377,18 @@
/// Return the end of the live range.
SlotIndex leaveIntvAtTop(MachineBasicBlock &MBB);
+ /// overlapIntv - Indicate that all instructions in range should use the open
+ /// interval, but also let the complement interval be live.
+ ///
+ /// This doubles the register pressure, but is sometimes required to deal with
+ /// register uses after the last valid split point.
+ ///
+ /// The Start index should be a return value from a leaveIntv* call, and End
+ /// should be in the same basic block. The parent interval must have the same
+ /// value across the range.
+ ///
+ void overlapIntv(SlotIndex Start, SlotIndex End);
+
/// closeIntv - Indicate that we are done editing the currently open
/// LiveInterval, and ranges can be trimmed.
void closeIntv();