AMDGPU: Clear offset register when using local stack area

eliminateFrameIndex won't fix up the offset register when the direct
frame index reference is moved to a separate move instruction. Switch
the offset to a base 0 (which it probably should be to begin with).

Author: arsenm

llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp

@@ -503,8 +503,10 @@ void SIRegisterInfo::resolveFrameIndex(MachineInstr &MI, Register BaseReg,
 #endif
   assert(FIOp && FIOp->isFI() && "frame index must be address operand");
   assert(TII->isMUBUF(MI));
-  assert(TII->getNamedOperand(MI, AMDGPU::OpName::soffset)->getReg() ==
-         MF->getInfo<SIMachineFunctionInfo>()->getStackPtrOffsetReg() &&
+
+  MachineOperand *SOffset = TII->getNamedOperand(MI, AMDGPU::OpName::soffset);
+  assert(SOffset->getReg() ==
+             MF->getInfo<SIMachineFunctionInfo>()->getStackPtrOffsetReg() &&
          "should only be seeing stack pointer offset relative FrameIndex");
 
   MachineOperand *OffsetOp = TII->getNamedOperand(MI, AMDGPU::OpName::offset);
@@ -513,6 +515,10 @@ void SIRegisterInfo::resolveFrameIndex(MachineInstr &MI, Register BaseReg,
 
   FIOp->ChangeToRegister(BaseReg, false);
   OffsetOp->setImm(NewOffset);
+
+  // The move materializing the base address will be an absolute stack address,
+  // so clear the base offset.
+  SOffset->ChangeToImmediate(0);
 }
 
 bool SIRegisterInfo::isFrameOffsetLegal(const MachineInstr *MI,

llvm/test/CodeGen/AMDGPU/local-stack-alloc-block-sp-reference.ll

@@ -41,8 +41,8 @@ define amdgpu_kernel void @local_stack_offset_uses_sp(i64 addrspace(1)* %out, i8
 ; GCN-NEXT:    v_add_u32_e32 v1, 0x20d0, v1
 ; GCN-NEXT:    buffer_load_dword v2, v1, s[0:3], 0 offen
 ; GCN-NEXT:    buffer_load_dword v1, v1, s[0:3], 0 offen offset:4
-; GCN-NEXT:    buffer_load_dword v3, v0, s[0:3], s32 offen
-; GCN-NEXT:    buffer_load_dword v4, v0, s[0:3], s32 offen offset:4
+; GCN-NEXT:    buffer_load_dword v3, v0, s[0:3], 0 offen
+; GCN-NEXT:    buffer_load_dword v4, v0, s[0:3], 0 offen offset:4
 ; GCN-NEXT:    s_waitcnt vmcnt(1)
 ; GCN-NEXT:    v_add_co_u32_e32 v0, vcc, v2, v3
 ; GCN-NEXT:    s_waitcnt lgkmcnt(0)
@@ -94,8 +94,8 @@ define void @func_local_stack_offset_uses_sp(i64 addrspace(1)* %out, i8 addrspac
 ; GCN-NEXT:    v_add_u32_e32 v3, 0x20d0, v3
 ; GCN-NEXT:    buffer_load_dword v4, v3, s[0:3], 0 offen
 ; GCN-NEXT:    buffer_load_dword v3, v3, s[0:3], 0 offen offset:4
-; GCN-NEXT:    buffer_load_dword v5, v2, s[0:3], s32 offen
-; GCN-NEXT:    buffer_load_dword v6, v2, s[0:3], s32 offen offset:4
+; GCN-NEXT:    buffer_load_dword v5, v2, s[0:3], 0 offen
+; GCN-NEXT:    buffer_load_dword v6, v2, s[0:3], 0 offen offset:4
 ; GCN-NEXT:    s_sub_u32 s32, s32, 0x180000
 ; GCN-NEXT:    s_mov_b32 s33, s5
 ; GCN-NEXT:    s_waitcnt vmcnt(1)

llvm/test/CodeGen/AMDGPU/stack-pointer-offset-relative-frameindex.ll

@@ -41,8 +41,9 @@ define amdgpu_kernel void @kernel_background_evaluate(float addrspace(5)* %kg, <
 ; GCN-NEXT:    s_and_saveexec_b32 s0, vcc_lo
 ; GCN-NEXT:    s_cbranch_execz BB0_2
 ; GCN-NEXT:  ; %bb.1: ; %if.then4.i
-; GCN-NEXT:    buffer_load_dword v0, v40, s[36:39], s32 offen
-; GCN-NEXT:    buffer_load_dword v1, v40, s[36:39], s32 offen offset:4
+; GCN-NEXT:    s_clause 0x1
+; GCN-NEXT:    buffer_load_dword v0, v40, s[36:39], 0 offen
+; GCN-NEXT:    buffer_load_dword v1, v40, s[36:39], 0 offen offset:4
 ; GCN-NEXT:    s_waitcnt vmcnt(0)
 ; GCN-NEXT:    v_add_nc_u32_e32 v0, v1, v0
 ; GCN-NEXT:    v_mul_lo_u32 v0, 0x41c64e6d, v0