TRI: Add hook to pass scavenger during frame elimination

The scavenger was not passed if requiresFrameIndexScavenging was
enabled. I need to be able to test for the availability of an
unallocatable register here, so I can't create a virtual register for
it.

It might be better to just always use the scavenger and stop
creating virtual registers.

llvm-svn: 287843

llvm/include/llvm/Target/TargetRegisterInfo.h

@@ -813,6 +813,13 @@ public:
     return false;
   }
 
+  /// Returns true if the target requires using the RegScavenger directly for
+  /// frame elimination despite using requiresFrameIndexScavenging.
+  virtual bool requiresFrameIndexReplacementScavenging(
+      const MachineFunction &MF) const {
+    return false;
+  }
+
   /// Returns true if the target wants the LocalStackAllocation pass to be run
   /// and virtual base registers used for more efficient stack access.
   virtual bool requiresVirtualBaseRegisters(const MachineFunction &MF) const {

llvm/lib/CodeGen/PrologEpilogInserter.cpp

@@ -117,6 +117,10 @@ private:
   // TRI->requiresFrameIndexScavenging() for the current function.
   bool FrameIndexVirtualScavenging;
 
+  // Flag to control whether the scavenger should be passed even though
+  // FrameIndexVirtualScavenging is used.
+  bool FrameIndexEliminationScavenging;
+
   void calculateCallFrameInfo(MachineFunction &Fn);
   void calculateSaveRestoreBlocks(MachineFunction &Fn);
 
@@ -176,6 +180,8 @@ bool PEI::runOnMachineFunction(MachineFunction &Fn) {
 
   RS = TRI->requiresRegisterScavenging(Fn) ? new RegScavenger() : nullptr;
   FrameIndexVirtualScavenging = TRI->requiresFrameIndexScavenging(Fn);
+  FrameIndexEliminationScavenging = (RS && !FrameIndexVirtualScavenging) ||
+    TRI->requiresFrameIndexReplacementScavenging(Fn);
 
   // Calculate the MaxCallFrameSize and AdjustsStack variables for the
   // function's frame information. Also eliminates call frame pseudo
@@ -1046,7 +1052,8 @@ void PEI::replaceFrameIndices(MachineBasicBlock *BB, MachineFunction &Fn,
   unsigned FrameSetupOpcode = TII.getCallFrameSetupOpcode();
   unsigned FrameDestroyOpcode = TII.getCallFrameDestroyOpcode();
 
-  if (RS && !FrameIndexVirtualScavenging) RS->enterBasicBlock(*BB);
+  if (RS && FrameIndexEliminationScavenging)
+    RS->enterBasicBlock(*BB);
 
   bool InsideCallSequence = false;
 
@@ -1115,7 +1122,7 @@ void PEI::replaceFrameIndices(MachineBasicBlock *BB, MachineFunction &Fn,
       // use that target machine register info object to eliminate
       // it.
       TRI.eliminateFrameIndex(MI, SPAdj, i,
-                              FrameIndexVirtualScavenging ?  nullptr : RS);
+                              FrameIndexEliminationScavenging ?  RS : nullptr);
 
       // Reset the iterator if we were at the beginning of the BB.
       if (AtBeginning) {
@@ -1140,7 +1147,7 @@ void PEI::replaceFrameIndices(MachineBasicBlock *BB, MachineFunction &Fn,
     if (DoIncr && I != BB->end()) ++I;
 
     // Update register states.
-    if (RS && !FrameIndexVirtualScavenging && DidFinishLoop)
+    if (RS && FrameIndexEliminationScavenging && DidFinishLoop)
       RS->forward(MI);
   }
 }

llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp

@@ -182,6 +182,16 @@ SIRegisterInfo::requiresFrameIndexScavenging(const MachineFunction &MF) const {
   return MF.getFrameInfo().hasStackObjects();
 }
 
+bool SIRegisterInfo::requiresFrameIndexReplacementScavenging(
+  const MachineFunction &MF) const {
+  // m0 is needed for the scalar store offset. m0 is unallocatable, so we can't
+  // create a virtual register for it during frame index elimination, so the
+  // scavenger is directly needed.
+  return MF.getFrameInfo().hasStackObjects() &&
+         MF.getSubtarget<SISubtarget>().hasScalarStores() &&
+         MF.getInfo<SIMachineFunctionInfo>()->hasSpilledSGPRs();
+}
+
 bool SIRegisterInfo::requiresVirtualBaseRegisters(
   const MachineFunction &) const {
   // There are no special dedicated stack or frame pointers.

llvm/lib/Target/AMDGPU/SIRegisterInfo.h

@@ -50,8 +50,9 @@ public:
 
   bool requiresRegisterScavenging(const MachineFunction &Fn) const override;
 
-
   bool requiresFrameIndexScavenging(const MachineFunction &MF) const override;
+  bool requiresFrameIndexReplacementScavenging(
+    const MachineFunction &MF) const override;
   bool requiresVirtualBaseRegisters(const MachineFunction &Fn) const override;
   bool trackLivenessAfterRegAlloc(const MachineFunction &MF) const override;