[LoongArch] Optimize conditional selection of integer

This patch optimizes code generation by leveraging the zeroing behavior of the `maskeqz`/`masknez` instructions.

```
int sel(int a, int b)
{
    return (a < b) ? a : 0;
}
```

```
slt	$a1,$a0,$a1
masknez	$a2,$r0,$a1
maskeqz	$a0,$a0,$a1
or	$a0,$a0,$a2
```

=>

```
slt	$a1,$a0,$a1
maskeqz	$a0,$a0,$a1
```

Reviewed By: SixWeining

Differential Revision: https://reviews.llvm.org/D153193

Author: SixWeining

llvm/lib/Target/LoongArch/LoongArchInstrInfo.td

@@ -1201,6 +1201,8 @@ def : Pat<(setle GPR:$rj, GPR:$rk), (XORI (SLT GPR:$rk, GPR:$rj), 1)>;
 
 /// Select
 
+def : Pat<(select GPR:$cond, GPR:$t, 0), (MASKEQZ GPR:$t, GPR:$cond)>;
+def : Pat<(select GPR:$cond, 0, GPR:$f), (MASKNEZ GPR:$f, GPR:$cond)>;
 def : Pat<(select GPR:$cond, GPR:$t, GPR:$f),
           (OR (MASKEQZ GPR:$t, GPR:$cond), (MASKNEZ GPR:$f, GPR:$cond))>;
 

llvm/test/CodeGen/LoongArch/atomicrmw-uinc-udec-wrap.ll

@@ -22,8 +22,6 @@ define i8 @atomicrmw_uinc_wrap_i8(ptr %ptr, i8 %val) {
 ; LA64-NEXT:    addi.d $a5, $a5, 1
 ; LA64-NEXT:    xori $a6, $a6, 1
 ; LA64-NEXT:    masknez $a5, $a5, $a6
-; LA64-NEXT:    maskeqz $a6, $zero, $a6
-; LA64-NEXT:    or $a5, $a6, $a5
 ; LA64-NEXT:    andi $a5, $a5, 255
 ; LA64-NEXT:    sll.w $a5, $a5, $a0
 ; LA64-NEXT:    and $a6, $a3, $a4
@@ -77,8 +75,6 @@ define i16 @atomicrmw_uinc_wrap_i16(ptr %ptr, i16 %val) {
 ; LA64-NEXT:    addi.d $a5, $a5, 1
 ; LA64-NEXT:    xori $a6, $a6, 1
 ; LA64-NEXT:    masknez $a5, $a5, $a6
-; LA64-NEXT:    maskeqz $a6, $zero, $a6
-; LA64-NEXT:    or $a5, $a6, $a5
 ; LA64-NEXT:    bstrpick.d $a5, $a5, 15, 0
 ; LA64-NEXT:    sll.w $a5, $a5, $a0
 ; LA64-NEXT:    and $a6, $a3, $a4
@@ -123,8 +119,6 @@ define i32 @atomicrmw_uinc_wrap_i32(ptr %ptr, i32 %val) {
 ; LA64-NEXT:    xori $a1, $a1, 1
 ; LA64-NEXT:    addi.d $a4, $a3, 1
 ; LA64-NEXT:    masknez $a4, $a4, $a1
-; LA64-NEXT:    maskeqz $a1, $zero, $a1
-; LA64-NEXT:    or $a4, $a1, $a4
 ; LA64-NEXT:  .LBB2_3: # %atomicrmw.start
 ; LA64-NEXT:    # Parent Loop BB2_1 Depth=1
 ; LA64-NEXT:    # => This Inner Loop Header: Depth=2
@@ -164,8 +158,6 @@ define i64 @atomicrmw_uinc_wrap_i64(ptr %ptr, i64 %val) {
 ; LA64-NEXT:    xori $a2, $a2, 1
 ; LA64-NEXT:    addi.d $a4, $a3, 1
 ; LA64-NEXT:    masknez $a4, $a4, $a2
-; LA64-NEXT:    maskeqz $a2, $zero, $a2
-; LA64-NEXT:    or $a4, $a2, $a4
 ; LA64-NEXT:  .LBB3_3: # %atomicrmw.start
 ; LA64-NEXT:    # Parent Loop BB3_1 Depth=1
 ; LA64-NEXT:    # => This Inner Loop Header: Depth=2

llvm/test/CodeGen/LoongArch/ir-instruction/select-bare-int.ll

@@ -106,3 +106,35 @@ define i64 @bare_select_i64(i1 %a, i64 %b, i64 %c) {
   %res = select i1 %a, i64 %b, i64 %c
   ret i64 %res
 }
+
+define i16 @bare_select_zero_i16(i1 %a, i16 %b) {
+; LA32-LABEL: bare_select_zero_i16:
+; LA32:       # %bb.0:
+; LA32-NEXT:    andi $a0, $a0, 1
+; LA32-NEXT:    masknez	$a0, $a1, $a0
+; LA32-NEXT:    ret
+;
+; LA64-LABEL: bare_select_zero_i16:
+; LA64:       # %bb.0:
+; LA64-NEXT:    andi $a0, $a0, 1
+; LA64-NEXT:    masknez	$a0, $a1, $a0
+; LA64-NEXT:    ret
+  %res = select i1 %a, i16 0, i16 %b
+  ret i16 %res
+}
+
+define i32 @bare_select_zero_i32(i1 %a, i32 %b) {
+; LA32-LABEL: bare_select_zero_i32:
+; LA32:       # %bb.0:
+; LA32-NEXT:    andi $a0, $a0, 1
+; LA32-NEXT:    maskeqz $a0, $a1, $a0
+; LA32-NEXT:    ret
+;
+; LA64-LABEL: bare_select_zero_i32:
+; LA64:       # %bb.0:
+; LA64-NEXT:    andi $a0, $a0, 1
+; LA64-NEXT:    maskeqz $a0, $a1, $a0
+; LA64-NEXT:    ret
+  %res = select i1 %a, i32 %b, i32 0
+  ret i32 %res
+}