[AMDGPU] Promote constant offset to the immediate by finding a new base with 13bit constant offset from the nearby instructions.

Summary: Promote constant offset to immediate by recomputing the relative 13bit offset from nearby instructions.
 E.g.
  s_movk_i32 s0, 0x1800
  v_add_co_u32_e32 v0, vcc, s0, v2
  v_addc_co_u32_e32 v1, vcc, 0, v6, vcc

  s_movk_i32 s0, 0x1000
  v_add_co_u32_e32 v5, vcc, s0, v2
  v_addc_co_u32_e32 v6, vcc, 0, v6, vcc
  global_load_dwordx2 v[5:6], v[5:6], off
  global_load_dwordx2 v[0:1], v[0:1], off
  =>
  s_movk_i32 s0, 0x1000
  v_add_co_u32_e32 v5, vcc, s0, v2
  v_addc_co_u32_e32 v6, vcc, 0, v6, vcc
  global_load_dwordx2 v[5:6], v[5:6], off
  global_load_dwordx2 v[0:1], v[5:6], off offset:2048

Author: FarhanaAleen

Reviewed By: arsenm, rampitec

Subscribers: llvm-commits, AMDGPU

Differential Revision: https://reviews.llvm.org/D55539

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@349196 91177308-0d34-0410-b5e6-96231b3b80d8

Author: Farhana Aleen

lib/Target/AMDGPU/SIISelLowering.h

@@ -170,7 +170,6 @@ class SITargetLowering final : public AMDGPUTargetLowering {
   SDValue performRcpCombine(SDNode *N, DAGCombinerInfo &DCI) const;
 
   bool isLegalFlatAddressingMode(const AddrMode &AM) const;
-  bool isLegalGlobalAddressingMode(const AddrMode &AM) const;
   bool isLegalMUBUFAddressingMode(const AddrMode &AM) const;
 
   unsigned isCFIntrinsic(const SDNode *Intr) const;
@@ -212,6 +211,7 @@ class SITargetLowering final : public AMDGPUTargetLowering {
                             SmallVectorImpl<Value*> &/*Ops*/,
                             Type *&/*AccessTy*/) const override;
 
+  bool isLegalGlobalAddressingMode(const AddrMode &AM) const;
   bool isLegalAddressingMode(const DataLayout &DL, const AddrMode &AM, Type *Ty,
                              unsigned AS,
                              Instruction *I = nullptr) const override;