Provide a target override for the cost of using a callee-saved register
for the first time.
Thanks Andy for the discussion.
rdar://16162005
llvm-svn: 204979
diff --git a/llvm/include/llvm/Target/TargetRegisterInfo.h b/llvm/include/llvm/Target/TargetRegisterInfo.h
index b3dbb9c..53fa7ca 100644
--- a/llvm/include/llvm/Target/TargetRegisterInfo.h
+++ b/llvm/include/llvm/Target/TargetRegisterInfo.h
@@ -689,6 +689,11 @@
/// debugging downstream codegen failures exposed by regalloc.
virtual bool mayOverrideLocalAssignment() const { return true; }
+ /// Allow the target to override the cost of using a callee-saved register for
+ /// the first time. Default value of 0 means we will use a callee-saved
+ /// register if it is available.
+ virtual unsigned getCSRFirstUseCost() const { return 0; }
+
/// requiresRegisterScavenging - returns true if the target requires (and can
/// make use of) the register scavenger.
virtual bool requiresRegisterScavenging(const MachineFunction &MF) const {
diff --git a/llvm/lib/CodeGen/RegAllocGreedy.cpp b/llvm/lib/CodeGen/RegAllocGreedy.cpp
index 0eb91ab..6a623b8 100644
--- a/llvm/lib/CodeGen/RegAllocGreedy.cpp
+++ b/llvm/lib/CodeGen/RegAllocGreedy.cpp
@@ -2123,7 +2123,10 @@
unsigned PhysReg,
unsigned &CostPerUseLimit,
SmallVectorImpl<unsigned> &NewVRegs) {
- BlockFrequency CSRCost(CSRFirstTimeCost);
+ // We use the larger one out of the command-line option and the value report
+ // by TRI.
+ BlockFrequency CSRCost(std::max((unsigned)CSRFirstTimeCost,
+ TRI->getCSRFirstUseCost()));
if (getStage(VirtReg) == RS_Spill && VirtReg.isSpillable()) {
// We choose spill over using the CSR for the first time if the spill cost
// is lower than CSRCost.
@@ -2172,7 +2175,8 @@
// When NewVRegs is not empty, we may have made decisions such as evicting
// a virtual register, go with the earlier decisions and use the physical
// register.
- if (CSRFirstTimeCost > 0 && CSRFirstUse && NewVRegs.empty()) {
+ if ((CSRFirstTimeCost || TRI->getCSRFirstUseCost()) &&
+ CSRFirstUse && NewVRegs.empty()) {
unsigned CSRReg = tryAssignCSRFirstTime(VirtReg, Order, PhysReg,
CostPerUseLimit, NewVRegs);
if (CSRReg || !NewVRegs.empty())