Hoist spills within a basic block.
Try to move spills as early as possible in their basic block. This can
help eliminate interferences by shortening the live range being
spilled.
This fixes PR10221.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@134776 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/InlineSpiller.cpp b/lib/CodeGen/InlineSpiller.cpp
index 4bd35c3..44e87ae 100644
--- a/lib/CodeGen/InlineSpiller.cpp
+++ b/lib/CodeGen/InlineSpiller.cpp
@@ -303,7 +303,8 @@
// Best spill candidate seen so far. This must dominate UseVNI.
SibValueInfo SVI(UseReg, UseVNI);
MachineBasicBlock *UseMBB = LIS.getMBBFromIndex(UseVNI->def);
- unsigned SpillDepth = Loops.getLoopDepth(UseMBB);
+ MachineBasicBlock *SpillMBB = UseMBB;
+ unsigned SpillDepth = Loops.getLoopDepth(SpillMBB);
bool SeenOrigPHI = false; // Original PHI met.
do {
@@ -316,15 +317,39 @@
// Is this value a better spill candidate?
if (!isRegToSpill(Reg)) {
MachineBasicBlock *MBB = LIS.getMBBFromIndex(VNI->def);
- if (MBB != UseMBB && MDT.dominates(MBB, UseMBB)) {
+ if (MBB == SpillMBB) {
+ // This is an alternative def earlier in the same MBB.
+ // Hoist the spill as far as possible in SpillMBB. This can ease
+ // register pressure:
+ //
+ // x = def
+ // y = use x
+ // s = copy x
+ //
+ // Hoisting the spill of s to immediately after the def removes the
+ // interference between x and y:
+ //
+ // x = def
+ // spill x
+ // y = use x<kill>
+ //
+ if (VNI->def < SVI.SpillVNI->def) {
+ DEBUG(dbgs() << " hoist in BB#" << MBB->getNumber() << ": "
+ << PrintReg(Reg) << ':' << VNI->id << '@' << VNI->def
+ << '\n');
+ SVI.SpillReg = Reg;
+ SVI.SpillVNI = VNI;
+ }
+ } else if (MBB != UseMBB && MDT.dominates(MBB, UseMBB)) {
// This is a valid spill location dominating UseVNI.
// Prefer to spill at a smaller loop depth.
unsigned Depth = Loops.getLoopDepth(MBB);
- if (Depth < SpillDepth) {
+ if (Depth <= SpillDepth) {
DEBUG(dbgs() << " spill depth " << Depth << ": " << PrintReg(Reg)
<< ':' << VNI->id << '@' << VNI->def << '\n');
SVI.SpillReg = Reg;
SVI.SpillVNI = VNI;
+ SpillMBB = MBB;
SpillDepth = Depth;
}
}