[AArch64][GlobalISel] Fix incorrect codegen for <16 x s8> G_ASHR.

Fixes PR49904

Author: aemerson

llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp

@@ -1791,7 +1791,7 @@ bool AArch64InstructionSelector::selectVectorAshrLshr(
     NegOpc = AArch64::NEGv8i16;
   } else if (Ty == LLT::vector(16, 8)) {
     Opc = IsASHR ? AArch64::SSHLv16i8 : AArch64::USHLv16i8;
-    NegOpc = AArch64::NEGv8i16;
+    NegOpc = AArch64::NEGv16i8;
   } else if (Ty == LLT::vector(8, 8)) {
     Opc = IsASHR ? AArch64::SSHLv8i8 : AArch64::USHLv8i8;
     NegOpc = AArch64::NEGv8i8;

llvm/test/CodeGen/AArch64/GlobalISel/select-vector-shift.mir

@@ -562,8 +562,8 @@ body:             |
     ; CHECK: liveins: $q0, $q1
     ; CHECK: [[COPY:%[0-9]+]]:fpr128 = COPY $q0
     ; CHECK: [[COPY1:%[0-9]+]]:fpr128 = COPY $q1
-    ; CHECK: [[NEGv8i16_:%[0-9]+]]:fpr128 = NEGv8i16 [[COPY1]]
-    ; CHECK: [[USHLv16i8_:%[0-9]+]]:fpr128 = USHLv16i8 [[COPY]], [[NEGv8i16_]]
+    ; CHECK: [[NEGv16i8_:%[0-9]+]]:fpr128 = NEGv16i8 [[COPY1]]
+    ; CHECK: [[USHLv16i8_:%[0-9]+]]:fpr128 = USHLv16i8 [[COPY]], [[NEGv16i8_]]
     ; CHECK: $q0 = COPY [[USHLv16i8_]]
     ; CHECK: RET_ReallyLR implicit $q0
     %0:fpr(<16 x s8>) = COPY $q0