[LoongArch] Optimize codegen for ISD::ROTL (#100344)

The LoongArch rotr.{w,d} instruction ignores the high bits of the shift
operand, allowing it to generate more efficient code using the constant
zero register.

Author: heiher

llvm/lib/Target/LoongArch/LoongArchInstrInfo.td

@@ -1123,7 +1123,7 @@ def : PatGprGpr<urem, MOD_WU>;
 def : PatGprGpr<mul, MUL_W>;
 def : PatGprGpr<mulhs, MULH_W>;
 def : PatGprGpr<mulhu, MULH_WU>;
-def : PatGprGpr<rotr, ROTR_W>;
+def : PatGprGpr<shiftop<rotr>, ROTR_W>;
 def : PatGprImm<rotr, ROTRI_W, uimm5>;
 
 foreach Idx = 1...3 in {
@@ -1146,8 +1146,8 @@ def : PatGprGpr<srem, MOD_D>;
 def : PatGprGpr_32<srem, MOD_W>;
 def : PatGprGpr<urem, MOD_DU>;
 def : PatGprGpr<loongarch_mod_wu, MOD_WU>;
-def : PatGprGpr<rotr, ROTR_D>;
-def : PatGprGpr<loongarch_rotr_w, ROTR_W>;
+def : PatGprGpr<shiftop<rotr>, ROTR_D>;
+def : PatGprGpr<shiftopw<loongarch_rotr_w>, ROTR_W>;
 def : PatGprImm<rotr, ROTRI_D, uimm6>;
 def : PatGprImm_32<rotr, ROTRI_W, uimm5>;
 def : PatGprImm<loongarch_rotr_w, ROTRI_W, uimm5>;

llvm/test/CodeGen/LoongArch/rotl-rotr.ll

@@ -5,15 +5,13 @@
 define signext i32 @rotl_32(i32 signext %x, i32 signext %y) nounwind {
 ; LA32-LABEL: rotl_32:
 ; LA32:       # %bb.0:
-; LA32-NEXT:    ori $a2, $zero, 32
-; LA32-NEXT:    sub.w $a1, $a2, $a1
+; LA32-NEXT:    sub.w $a1, $zero, $a1
 ; LA32-NEXT:    rotr.w $a0, $a0, $a1
 ; LA32-NEXT:    ret
 ;
 ; LA64-LABEL: rotl_32:
 ; LA64:       # %bb.0:
-; LA64-NEXT:    ori $a2, $zero, 32
-; LA64-NEXT:    sub.d $a1, $a2, $a1
+; LA64-NEXT:    sub.d $a1, $zero, $a1
 ; LA64-NEXT:    rotr.w $a0, $a0, $a1
 ; LA64-NEXT:    ret
   %z = sub i32 32, %y
@@ -80,8 +78,7 @@ define i64 @rotl_64(i64 %x, i64 %y) nounwind {
 ;
 ; LA64-LABEL: rotl_64:
 ; LA64:       # %bb.0:
-; LA64-NEXT:    ori $a2, $zero, 64
-; LA64-NEXT:    sub.d $a1, $a2, $a1
+; LA64-NEXT:    sub.d $a1, $zero, $a1
 ; LA64-NEXT:    rotr.d $a0, $a0, $a1
 ; LA64-NEXT:    ret
   %z = sub i64 64, %y
@@ -149,8 +146,7 @@ define signext i32 @rotl_32_mask(i32 signext %x, i32 signext %y) nounwind {
 ;
 ; LA64-LABEL: rotl_32_mask:
 ; LA64:       # %bb.0:
-; LA64-NEXT:    ori $a2, $zero, 32
-; LA64-NEXT:    sub.d $a1, $a2, $a1
+; LA64-NEXT:    sub.d $a1, $zero, $a1
 ; LA64-NEXT:    rotr.w $a0, $a0, $a1
 ; LA64-NEXT:    ret
   %z = sub i32 0, %y
@@ -170,8 +166,7 @@ define signext i32 @rotl_32_mask_and_63_and_31(i32 signext %x, i32 signext %y) n
 ;
 ; LA64-LABEL: rotl_32_mask_and_63_and_31:
 ; LA64:       # %bb.0:
-; LA64-NEXT:    ori $a2, $zero, 32
-; LA64-NEXT:    sub.d $a1, $a2, $a1
+; LA64-NEXT:    sub.d $a1, $zero, $a1
 ; LA64-NEXT:    rotr.w $a0, $a0, $a1
 ; LA64-NEXT:    ret
   %a = and i32 %y, 63
@@ -192,8 +187,7 @@ define signext i32 @rotl_32_mask_or_64_or_32(i32 signext %x, i32 signext %y) nou
 ;
 ; LA64-LABEL: rotl_32_mask_or_64_or_32:
 ; LA64:       # %bb.0:
-; LA64-NEXT:    ori $a2, $zero, 32
-; LA64-NEXT:    sub.d $a1, $a2, $a1
+; LA64-NEXT:    sub.d $a1, $zero, $a1
 ; LA64-NEXT:    rotr.w $a0, $a0, $a1
 ; LA64-NEXT:    ret
   %a = or i32 %y, 64