handle illegal offset but fits in si12

Author: tangaac

llvm/lib/Target/LoongArch/LoongArchRegisterInfo.cpp

@@ -140,36 +140,48 @@ bool LoongArchRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
 
   bool FrameRegIsKill = false;
 
-  int fixed_offset = Offset.getFixed();
-  bool OffsetLegal = false;
+  int FixedOffset = Offset.getFixed();
+  bool OffsetLegal = true;
 
-  // Handle offsets that exceed the immediate range of the instruction
+  // Handle offsets that exceed the immediate range of the instruction.
   switch (MIOpc) {
   case LoongArch::VSTELM_B:
   case LoongArch::XVSTELM_B: {
-    OffsetLegal = isInt<8>(fixed_offset);
+    OffsetLegal = isInt<8>(FixedOffset);
     break;
   }
   case LoongArch::VSTELM_H:
   case LoongArch::XVSTELM_H: {
-    OffsetLegal = isShiftedInt<8, 1>(fixed_offset);
+    OffsetLegal = isShiftedInt<8, 1>(FixedOffset);
     break;
   }
   case LoongArch::VSTELM_W:
   case LoongArch::XVSTELM_W: {
-    OffsetLegal = isShiftedInt<8, 2>(fixed_offset);
+    OffsetLegal = isShiftedInt<8, 2>(FixedOffset);
     break;
   }
   case LoongArch::VSTELM_D:
   case LoongArch::XVSTELM_D: {
-    OffsetLegal = isShiftedInt<8, 3>(fixed_offset);
+    OffsetLegal = isShiftedInt<8, 3>(FixedOffset);
     break;
   }
-  default:
-    OffsetLegal = isInt<12>(fixed_offset);
   }
 
-  if (!OffsetLegal) {
+  if (!OffsetLegal && isInt<12>(FixedOffset)) {
+    unsigned Addi = IsLA64 ? LoongArch::ADDI_D : LoongArch::ADDI_W;
+
+    // The offset fits in si12 but is not legal for the instruction,
+    // so use only one scratch register instead.
+    Register ScratchReg = MRI.createVirtualRegister(&LoongArch::GPRRegClass);
+    BuildMI(MBB, II, DL, TII->get(Addi), ScratchReg)
+        .addReg(FrameReg)
+        .addImm(FixedOffset);
+    Offset = StackOffset::getFixed(0);
+    FrameReg = ScratchReg;
+    FrameRegIsKill = true;
+  }
+
+  if (!isInt<12>(FixedOffset)) {
     unsigned Addi = IsLA64 ? LoongArch::ADDI_D : LoongArch::ADDI_W;
     unsigned Add = IsLA64 ? LoongArch::ADD_D : LoongArch::ADD_W;
 

llvm/test/CodeGen/LoongArch/lasx/ir-instruction/extractelement.ll

@@ -227,8 +227,7 @@ define void @eliminate_frame_index(<8 x i32> %a) nounwind {
 ; CHECK-LABEL: eliminate_frame_index:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    addi.d $sp, $sp, -1040
-; CHECK-NEXT:    ori $a0, $zero, 524
-; CHECK-NEXT:    add.d $a0, $sp, $a0
+; CHECK-NEXT:    addi.d $a0, $sp, 524
 ; CHECK-NEXT:    xvstelm.w $xr0, $a0, 0, 1
 ; CHECK-NEXT:    addi.d $sp, $sp, 1040
 ; CHECK-NEXT:    ret

llvm/test/CodeGen/LoongArch/lsx/ir-instruction/extractelement.ll

@@ -167,8 +167,7 @@ define void @eliminate_frame_index(<4 x i32> %a) nounwind {
 ; CHECK-LABEL: eliminate_frame_index:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    addi.d $sp, $sp, -1040
-; CHECK-NEXT:    ori $a0, $zero, 524
-; CHECK-NEXT:    add.d $a0, $sp, $a0
+; CHECK-NEXT:    addi.d $a0, $sp, 524
 ; CHECK-NEXT:    vstelm.w $vr0, $a0, 0, 1
 ; CHECK-NEXT:    addi.d $sp, $sp, 1040
 ; CHECK-NEXT:    ret