[SDAG] Precommit tests for #126207 (NFC) (#126208)

Add missing test coverage for codepaths touched by #126207.

Author: c-rhodes

llvm/test/CodeGen/AArch64/memcpy-f128.ll

@@ -1,4 +1,5 @@
 ; RUN: llc < %s -mtriple=aarch64-linux-gnu | FileCheck %s
+; RUN: llc < %s -mtriple=aarch64-linux-gnu -mattr=-neon | FileCheck %s
 
 %structA = type { i128 }
 @stubA = internal unnamed_addr constant %structA zeroinitializer, align 8

llvm/test/CodeGen/ARM/memcpy-inline.ll

@@ -12,6 +12,7 @@
 @.str4 = private unnamed_addr constant [18 x i8] c"DHRYSTONE PROGR  \00", align 1
 @.str5 = private unnamed_addr constant [7 x i8] c"DHRYST\00", align 1
 @.str6 = private unnamed_addr constant [14 x i8] c"/tmp/rmXXXXXX\00", align 1
+@empty = private unnamed_addr constant [31 x i8] zeroinitializer, align 1
 @spool.splbuf = internal global [512 x i8] zeroinitializer, align 16
 
 define i32 @t0() {
@@ -282,5 +283,31 @@ entry:
   ret void
 }
 
+define void @copy_from_zero_constant(ptr nocapture %C) nounwind {
+; CHECK-LABEL: copy_from_zero_constant:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    vmov.i32 q8, #0x0
+; CHECK-NEXT:    movs r1, #15
+; CHECK-NEXT:    vst1.8 {d16, d17}, [r0], r1
+; CHECK-NEXT:    vst1.8 {d16, d17}, [r0]
+; CHECK-NEXT:    bx lr
+;
+; CHECK-T1-LABEL: copy_from_zero_constant:
+; CHECK-T1:       @ %bb.0: @ %entry
+; CHECK-T1-NEXT:    .save {r7, lr}
+; CHECK-T1-NEXT:    push {r7, lr}
+; CHECK-T1-NEXT:    ldr r1, .LCPI8_0
+; CHECK-T1-NEXT:    movs r2, #31
+; CHECK-T1-NEXT:    bl __aeabi_memcpy
+; CHECK-T1-NEXT:    pop {r7, pc}
+; CHECK-T1-NEXT:    .p2align 2
+; CHECK-T1-NEXT:  @ %bb.1:
+; CHECK-T1-NEXT:  .LCPI8_0:
+; CHECK-T1-NEXT:    .long .Lempty
+entry:
+  tail call void @llvm.memcpy.p0.p0.i64(ptr %C, ptr @empty, i64 31, i1 false)
+  ret void
+}
+
 declare void @llvm.memcpy.p0.p0.i32(ptr nocapture, ptr nocapture, i32, i1) nounwind
 declare void @llvm.memcpy.p0.p0.i64(ptr nocapture, ptr nocapture, i64, i1) nounwind