[AArch64] Fix crash caused by invalid vector element type

[NickGuy]

Summary

Fixes a crash caused by D91255, when LLVMTy is null when calling changeExtendedVectorElementType.

[fhahn]

this needs a test?

[NickGuy]

In D94234#2484467, @fhahn wrote:

this needs a test?

Possibly; Though it doesn't change the supported scope covered by the tests in D91255, it might be worth having one to make sure the crash doesn't reoccur.

[dmajor]

Confirmed this fixes our original full-size repro, thanks! I'll let those better knowledgeable than me review the change though.

[dmgreen]

LGTM thanks, but please try and simplify the test case if you can.

llvm/test/CodeGen/AArch64/aarch64-dup-ext-vectortype-crash.ll

13

Can this test be made simpler? It possibly just needs an extend from a non-expected type, splat into a mul.

[NickGuy]

llvm/test/CodeGen/AArch64/aarch64-dup-ext-vectortype-crash.ll

13

Done, thanks for the tip

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

static SDValue performCommonVectorExtendCombine(SDValue VectorShuffle,
   EVT TargetType = VectorShuffle.getValueType();
   EVT PreExtendType = calculatePreExtendType(Extend, DAG);
 
   if ((TargetType != MVT::v8i16 && TargetType != MVT::v4i32 &&
        TargetType != MVT::v2i64) ||
       (PreExtendType == MVT::Other))
     return SDValue();
 
+  // Restrict valid pre-extend data type
+  if (PreExtendType != MVT::i8 && PreExtendType != MVT::i16 &&
+      PreExtendType != MVT::i32)
+    return SDValue();
+
   EVT PreExtendVT = TargetType.changeVectorElementType(PreExtendType);
 
   if (PreExtendVT.getVectorElementCount() != TargetType.getVectorElementCount())
     return SDValue();
 
   if (TargetType.getScalarSizeInBits() != PreExtendVT.getScalarSizeInBits() * 2)
     return SDValue();
 

llvm/test/CodeGen/AArch64/aarch64-dup-ext-vectortype-crash.ll

+; RUN: llc < %s -mtriple aarch64-none-linux-gnu | FileCheck %s
+
+; This test covers a case where extended value types can't be converted to
+; vector types, resulting in a crash. We don't care about the specific output
+; here, only that this case no longer causes said crash.
+; See https://reviews.llvm.org/D91255#2484399 for context
+define <8 x i16> @extend_i7_v8i16(i7 %src, <8 x i8> %b) {
+; CHECK-LABEL: extend_i7_v8i16:
+entry:
+    %in = sext i7 %src to i16
+    %ext.b = sext <8 x i8> %b to <8 x i16>
+    %broadcast.splatinsert = insertelement <8 x i16> undef, i16 %in, i16 0
+    %broadcast.splat = shufflevector <8 x i16> %broadcast.splatinsert, <8 x i16> undef, <8 x i32> zeroinitializer
+    %out = mul nsw <8 x i16> %broadcast.splat, %ext.b
+    ret <8 x i16> %out
+}