[AMDGPU] Track physical VGPRs used for SGPR spills

Physical VGPRs used for SGPR spills need to be tracked independent
of WWM reserved registers.  The WWM reserved set contains extra
registers allocated during WWM pre-allocation pass.

This causes SGPR spills allocated after WWM pre-allocation to
overlap with WWM register usage, e.g. if frame pointer is
spilt during prologue/epilog insertion.

Author: perlfu

llvm/lib/Target/AMDGPU/SIMachineFunctionInfo.cpp

@@ -349,8 +349,9 @@ bool SIMachineFunctionInfo::allocatePhysicalVGPRForSGPRSpills(
       MBB.addLiveIn(LaneVGPR);
       MBB.sortUniqueLiveIns();
     }
+    SpillPhysVGPRs.push_back(LaneVGPR);
   } else {
-    LaneVGPR = WWMReservedRegs.back();
+    LaneVGPR = SpillPhysVGPRs.back();
   }
 
   SGPRSpillsToPhysicalVGPRLanes[FI].push_back(

llvm/lib/Target/AMDGPU/SIMachineFunctionInfo.h

@@ -502,6 +502,7 @@ class SIMachineFunctionInfo final : public AMDGPUMachineFunction,
   unsigned NumVirtualVGPRSpillLanes = 0;
   unsigned NumPhysicalVGPRSpillLanes = 0;
   SmallVector<Register, 2> SpillVGPRs;
+  SmallVector<Register, 2> SpillPhysVGPRs;
   using WWMSpillsMap = MapVector<Register, int>;
   // To track the registers used in instructions that can potentially modify the
   // inactive lanes. The WWM instructions and the writelane instructions for

llvm/test/CodeGen/AMDGPU/sgpr-spill-overlap-wwm-reserve.mir

@@ -39,7 +39,7 @@ body:             |
   ; GCN-NEXT:   SCRATCH_STORE_DWORD_SADDR $vgpr5, $sgpr33, 12, 0, implicit $exec, implicit $flat_scr :: (store (s32) into %stack.72, addrspace 5)
   ; GCN-NEXT:   SCRATCH_STORE_DWORD_SADDR killed $vgpr4, $sgpr33, 16, 0, implicit $exec, implicit $flat_scr :: (store (s32) into %stack.74, addrspace 5)
   ; GCN-NEXT:   $exec_lo = S_MOV_B32 killed $sgpr1
-  ; GCN-NEXT:   $vgpr4 = SI_SPILL_S32_TO_VGPR $sgpr0, 4, undef $vgpr4
+  ; GCN-NEXT:   $vgpr3 = SI_SPILL_S32_TO_VGPR $sgpr0, 4, undef $vgpr3
   ; GCN-NEXT:   $sgpr32 = frame-setup S_ADD_I32 $sgpr32, 24, implicit-def dead $scc
   ; GCN-NEXT:   renamable $vgpr5 = IMPLICIT_DEF
   ; GCN-NEXT:   $vgpr1 = SI_SPILL_S32_TO_VGPR $sgpr4, 0, $vgpr1
@@ -198,7 +198,7 @@ body:             |
   ; GCN-NEXT:   $sgpr5 = SI_RESTORE_S32_FROM_VGPR $vgpr1, 1
   ; GCN-NEXT:   $sgpr4 = SI_RESTORE_S32_FROM_VGPR $vgpr1, 0
   ; GCN-NEXT:   KILL killed renamable $vgpr5
-  ; GCN-NEXT:   $sgpr0 = SI_RESTORE_S32_FROM_VGPR $vgpr4, 4
+  ; GCN-NEXT:   $sgpr0 = SI_RESTORE_S32_FROM_VGPR $vgpr3, 4
   ; GCN-NEXT:   $sgpr1 = S_XOR_SAVEEXEC_B32 -1, implicit-def $exec, implicit-def dead $scc, implicit $exec
   ; GCN-NEXT:   $vgpr1 = SCRATCH_LOAD_DWORD_SADDR $sgpr33, 0, 0, implicit $exec, implicit $flat_scr :: (load (s32) from %stack.69, addrspace 5)
   ; GCN-NEXT:   $vgpr2 = SCRATCH_LOAD_DWORD_SADDR $sgpr33, 4, 0, implicit $exec, implicit $flat_scr :: (load (s32) from %stack.70, addrspace 5)