[LoongArch] Fix incorrect logic in isLegalAddressingMode() (#88694)

This will adress issue:
ClangBuiltLinux/linux#2014

Author: wangleiat

llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp

@@ -4876,28 +4876,27 @@ bool LoongArchTargetLowering::isLegalAddressingMode(const DataLayout &DL,
   if (AM.BaseGV)
     return false;
 
-  // Require a 12 or 14 bit signed offset.
-  if (!isInt<12>(AM.BaseOffs) || !isShiftedInt<14, 2>(AM.BaseOffs))
+  // Require a 12-bit signed offset or 14-bit signed offset left-shifted by 2
+  // with `UAL` feature.
+  if (!isInt<12>(AM.BaseOffs) &&
+      !(isShiftedInt<14, 2>(AM.BaseOffs) && Subtarget.hasUAL()))
     return false;
 
   switch (AM.Scale) {
   case 0:
-    // "i" is not allowed.
-    if (!AM.HasBaseReg)
-      return false;
-    // Otherwise we have "r+i".
+    // "r+i" or just "i", depending on HasBaseReg.
     break;
   case 1:
     // "r+r+i" is not allowed.
-    if (AM.HasBaseReg && AM.BaseOffs != 0)
+    if (AM.HasBaseReg && AM.BaseOffs)
       return false;
     // Otherwise we have "r+r" or "r+i".
     break;
   case 2:
     // "2*r+r" or "2*r+i" is not allowed.
     if (AM.HasBaseReg || AM.BaseOffs)
       return false;
-    // Otherwise we have "r+r".
+    // Allow "2*r" as "r+r".
     break;
   default:
     return false;

llvm/test/CodeGen/LoongArch/gep-imm.ll

@@ -4,23 +4,19 @@
 define void @test(ptr %sp, ptr %t, i32 %n) {
 ; CHECK-LABEL: test:
 ; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    ld.d $a0, $a0, 0
 ; CHECK-NEXT:    move $a3, $zero
-; CHECK-NEXT:    ld.d $a4, $a0, 0
-; CHECK-NEXT:    lu12i.w $a0, 1
-; CHECK-NEXT:    ori $a5, $a0, 3904
-; CHECK-NEXT:    add.d $a0, $a1, $a5
-; CHECK-NEXT:    add.d $a1, $a4, $a5
 ; CHECK-NEXT:    addi.w $a2, $a2, 0
 ; CHECK-NEXT:    addi.w $a4, $a3, 0
 ; CHECK-NEXT:    bge $a4, $a2, .LBB0_2
 ; CHECK-NEXT:    .p2align 4, , 16
 ; CHECK-NEXT:  .LBB0_1: # %while_body
 ; CHECK-NEXT:    # =>This Inner Loop Header: Depth=1
 ; CHECK-NEXT:    addi.d $a4, $a3, 1
-; CHECK-NEXT:    st.w $a4, $a1, 0
-; CHECK-NEXT:    st.w $a3, $a1, 4
-; CHECK-NEXT:    st.w $a4, $a0, 0
-; CHECK-NEXT:    st.w $a3, $a0, 4
+; CHECK-NEXT:    stptr.w $a4, $a0, 8000
+; CHECK-NEXT:    stptr.w $a3, $a0, 8004
+; CHECK-NEXT:    stptr.w $a4, $a1, 8000
+; CHECK-NEXT:    stptr.w $a3, $a1, 8004
 ; CHECK-NEXT:    move $a3, $a4
 ; CHECK-NEXT:    addi.w $a4, $a3, 0
 ; CHECK-NEXT:    blt $a4, $a2, .LBB0_1