[AArch64] GlobalIsel unable to legalize vectorized binaryop(G_ADD, G_SUB, ...)

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Our aflplusplus fuzzing shows that AArch64 can't compile the following code can't compile using llc -mtriple=aarch64 -global-isel add.ll, It could complaint: unable to legalize instruction: %10:_(<32 x s16>) = G_ADD %0:_, %1:_ (in function: add_32xi16)

Godbolt: https://godbolt.org/z/7rz7WdbEx

define <32 x i16> @add_32xi16(<32 x i16> %0, <32 x i16> %1) {
    %3 = add <32 x i16> %0, %1
    ret <32 x i16> %3
}

define <64 x i8> @add_64xi8(<64 x i8> %0, <64 x i8> %1) {
    %3 = add <64 x i8> %0, %1
    ret <64 x i8> %3
}

A further study shows that in AArch64LegalizeInfo.cpp:116

  getActionDefinitionsBuilder({G_ADD, G_SUB, G_MUL, G_AND, G_OR, G_XOR})
      .legalFor({s32, s64, v2s32, v4s32, v4s16, v8s16, v16s8, v8s8})
      .scalarizeIf(
          [=](const LegalityQuery &Query) {
            return Query.Opcode == G_MUL && Query.Types[0] == v2s64;
          },
          0)
      .legalFor({v2s64})
      .widenScalarToNextPow2(0)
      .clampScalar(0, s32, s64)
      .clampNumElements(0, v2s32, v4s32)
      .clampNumElements(0, v2s64, v2s64)
      .moreElementsToNextPow2(0);

Many vectorized operations are not legal for all five operations.
It seems to us that we should be using the following diff:

@@ -121,8 +121,8 @@ AArch64LegalizerInfo::AArch64LegalizerInfo(const AArch64Subtarget &ST)
           },
           0)
       .legalFor({v2s64})
-      .widenScalarToNextPow2(0)
-      .clampScalar(0, s32, s64)
+      .widenScalarOrEltToNextPow2(0)
+      .clampScalarOrElt(0, s32, s64)
       .clampNumElements(0, v2s32, v4s32)
       .clampNumElements(0, v2s64, v2s64)
       .moreElementsToNextPow2(0);

However, many tests failed after we make this change. It seems many other places need to switch from clampScalar to clampScalarOrElt to include vector types.

Is this a feature, where we don't want certain vector types to get compiled; or this is a bug.
If it is a feature, can anyone elaborate why do we design it like this? If it is a bug, we can make some quick fixes.

[llvmbot]

@llvm/issue-subscribers-backend-aarch64

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@aemerson @fhahn Would it be possible for you to shed some light on this? For I am not sure how should we proceed from here.

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@aemerson @fhahn @llvm/issue-subscribers-backend-aarch64 Since I don't have time all the knowledge to fix this, do you thing it would be a good idea to push all the unimplemented features as xfail unit tests to keep track of them?

[aemerson]

Sorry for not responding to this, I'd missed it. Thanks for the report. I think your analysis is generally correct, this is just missing functionality.

[dzhidzhoev]

Fix https://reviews.llvm.org/D143517