[clang] [clang][cir] Add missing tests for SVE DUP intrinsics (PR #223932)

[Andrzej Warzyński via cfe-commits]

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@@ -398,7 +398,7 @@ mlir::Type CIRGenTypes::convertType(QualType type) {
                                         /*is_scalable=*/true);
       break;
     case BuiltinType::SveBFloat16:
-      resultType = cir::VectorType::get(builder.getFp16Ty(), 8,
+      resultType = cir::VectorType::get(builder.getBfloat16Ty(), 8,
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banach-space wrote:

Good question!

In most cases, we rely on LIT tests to verify the compiler (and to exercise every possible code path). For this particular line, I added the following test: https://github.com/llvm/llvm-project/blob/0c62d834abff9b180def1b32d3cf9c225d504994/clang/test/CodeGen/AArch64/sve/len.c?plain=1#L95-L105

Note that it does not verify that `bfloat` is used. It doesn't have to though - the input argument is not used (so we don't check it). Instead, what's key is that:
* `@llvm.vscale.i64()` is called to get the value of SVE's `vscale`.
* `vscale` is multiplied by `8`: `mul nuw i64 [[VSCALE]], 8` (there's `8` `bfloat` values in a 128-bit vector granule).

Since this PR adds tests that properly exercise `bfloat16`(see e.g. `test_svdup_n_bf16_z`), I have refrained from updating `test_svlen_bf16` (i.e. the original test). But ultimately, the bug sneaked it because the testing wasn't adequeate.

IMHO, it is neither possible nor desirable to check every single line of code (that would mean _a lot_ of tests and be very hard to maintain). LLVM tests tend to focus on what matters to users and there's so many of them that the coverage is actually pretty good (but not 100%). We do have gaps though and this is a very good example 😅 

https://github.com/llvm/llvm-project/pull/223932