[RegisterClassInfo] Invalidate the register pressure set limit cache when reserved regs or callee saved regs change

[craig.topper]

Summary

Currently we only invalidate the pressure set limit cached when the TargetRegisterInfo pointer changes. But as reserved regs and callee saved regs are used as part of calculating the limits we should invalidate when those change too.

I encountered this when reverting a patch from the 6.0 branch. One of the x86 test files had a function that used rbp as a frame pointer, making it reserved. It was followed by another function which didn't use rbp but had the same TRI so the pressure set limit cache was not invalidated. If i removed the function that used rbp as a frame pointer from the file, the remaining function then got a different register pressure limit for the GR16 pressure set. This caused the machine scheduler to change the scheduling for the function. This was an unexpected change from just deleting a function.

I don't have a test case for trunk because the particular x86 test case is different enough from the 6.0 branch to not be affected now.

[MatzeB]

LGTM

lib/CodeGen/RegisterClassInfo.cpp

 void RegisterClassInfo::runOnMachineFunction(const MachineFunction &mf) {
   bool Update = false;
   MF = &mf;
 
   // Allocate new array the first time we see a new target.
   if (MF->getSubtarget().getRegisterInfo() != TRI) {
     TRI = MF->getSubtarget().getRegisterInfo();
     RegClass.reset(new RCInfo[TRI->getNumRegClasses()]);
-    unsigned NumPSets = TRI->getNumRegPressureSets();
-    PSetLimits.reset(new unsigned[NumPSets]);
-    std::fill(&PSetLimits[0], &PSetLimits[NumPSets], 0);
     Update = true;
   }
 
   // Does this MF have different CSRs?
   assert(TRI && "no register info set");
 
   // Get the callee saved registers.
   const MCPhysReg *CSR = MF->getRegInfo().getCalleeSavedRegs();
void RegisterClassInfo::runOnMachineFunction(const MachineFunction &mf) {
   // Different reserved registers?
   const BitVector &RR = MF->getRegInfo().getReservedRegs();
   if (Reserved.size() != RR.size() || RR != Reserved) {
     Update = true;
     Reserved = RR;
   }
 
   // Invalidate cached information from previous function.
-  if (Update)
+  if (Update) {
+    unsigned NumPSets = TRI->getNumRegPressureSets();
+    PSetLimits.reset(new unsigned[NumPSets]);
+    std::fill(&PSetLimits[0], &PSetLimits[NumPSets], 0);
     ++Tag;
   }
+}
 
 /// compute - Compute the preferred allocation order for RC with reserved
 /// registers filtered out. Volatile registers come first followed by CSR
 /// aliases ordered according to the CSR order specified by the target.
 void RegisterClassInfo::compute(const TargetRegisterClass *RC) const {
   assert(RC && "no register class given");
   RCInfo &RCI = RegClass[RC->getID()];