[RISCV] Add test which shows alignment of constant pools and the functions which followed

[reames]

Summary

See next change in stack for context.

[asb]

LGTM.

[reames]

Motivating transform abandoned, and change reverted.

llvm/test/CodeGen/RISCV/rvv/fixed-vectors-constant-pool-alignment.ll

+; RUN: llc -mtriple=riscv64 -mattr=+v -verify-machineinstrs < %s | FileCheck %s
+
+define void @constantpool_v16xi8(ptr %x) {
+; CHECK: .section .rodata.cst16,"aM",@progbits,16
+; CHECK: .p2align 4, 0x0
+; CHECK: .byte
+; CHECK: .globl constantpool_v16xi8
+; CHECK: .p2align 2
+  store <16 x i8> <i8 0, i8 1, i8 3, i8 3, i8 4, i8 5, i8 15, i8 7, i8 27, i8 9, i8 10, i8 11, i8 12, i8 13, i8 12, i8 15>, ptr %x
+  ret void
+}
+
+define void @constantpool_v4xi32(ptr %x) {
+; CHECK: .section .rodata.cst16,"aM",@progbits,16
+; CHECK: .p2align 4, 0x0
+; CHECK: .word
+; CHECK: .globl constantpool_v4xi32
+; CHECK: .p2align 2
+  store <4 x i32> <i32 -27, i32 255, i32 3, i32 63>, ptr %x
+  ret void
+}
+
+; Note that to exercise the 64 bit alignment case, we need four elements
+; as all of the two element small constant cases get optimized to some
+; other sequence
+define void @constantpool_v4xi64(ptr %x) {
+; CHECK: .section .rodata.cst32,"aM",@progbits,32
+; CHECK: .p2align 5, 0x0
+; CHECK: .quad
+; CHECK: .globl constantpool_v4xi64
+; CHECK: .p2align 2
+  store <4 x i64> <i64 -27, i64 255, i64 3, i64 63>, ptr %x
+  ret void
+}
+
+define void @constantpool_i64(ptr %x) {
+; CHECK: .section .sdata,"aw",@progbits
+; CHECK: .p2align 3
+; CHECK: .quad  58373358938439
+; CHECK: .globl constantpool_i64
+; CHECK: .p2align 2
+  store i64 58373358938439, ptr %x
+  ret void
+}
+
+