[RISCV] Fix a codegen crash in getSetCCResultType

This patch fixes some crashes coming from
`RISCVISelLowering::getSetCCResultType`, which would occasionally return
an EVT constructed from an invalid MVT, which has a null Type pointer.

The attached test shows this happening currently for some fixed-length
vectors, which hit this issue when the V extension was enabled, even
though they're not legal types under the V extension. The fix was also
pre-emptively extended to scalable vectors which can't be represented as
an MVT, even though a test case couldn't be found for them.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D95434

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -481,12 +481,13 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
   }
 }
 
-EVT RISCVTargetLowering::getSetCCResultType(const DataLayout &DL, LLVMContext &,
+EVT RISCVTargetLowering::getSetCCResultType(const DataLayout &DL,
+                                            LLVMContext &Context,
                                             EVT VT) const {
   if (!VT.isVector())
     return getPointerTy(DL);
-  if (Subtarget.hasStdExtV())
-    return MVT::getVectorVT(MVT::i1, VT.getVectorElementCount());
+  if (Subtarget.hasStdExtV() && VT.isScalableVector())
+    return EVT::getVectorVT(Context, MVT::i1, VT.getVectorElementCount());
   return VT.changeVectorElementTypeToInteger();
 }
 

llvm/test/CodeGen/RISCV/vec3-setcc-crash.ll

@@ -0,0 +1,92 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=riscv32 -mattr=+experimental-v -verify-machineinstrs < %s \
+; RUN:     | FileCheck %s --check-prefix=RV32
+; RUN: llc -mtriple=riscv64 -mattr=+experimental-v -verify-machineinstrs < %s \
+; RUN:     | FileCheck %s --check-prefix=RV64
+
+; This test would lead one of the DAGCombiner's visitVSELECT optimizations to
+; call getSetCCResultType, from which we'd return an invalid MVT (<3 x i1>)
+; upon seeing that the V extension is enabled. The invalid MVT has a null
+; Type*, which then segfaulted when accessed (as an EVT).
+define void @vec3_setcc_crash(<3 x i8>* %in, <3 x i8>* %out) {
+; RV32-LABEL: vec3_setcc_crash:
+; RV32:       # %bb.0:
+; RV32-NEXT:    lw a0, 0(a0)
+; RV32-NEXT:    lui a2, 16
+; RV32-NEXT:    addi a2, a2, -256
+; RV32-NEXT:    and a2, a0, a2
+; RV32-NEXT:    slli a3, a2, 16
+; RV32-NEXT:    srai a6, a3, 24
+; RV32-NEXT:    slli a4, a0, 24
+; RV32-NEXT:    srai a3, a4, 24
+; RV32-NEXT:    slli a4, a0, 8
+; RV32-NEXT:    mv a5, a0
+; RV32-NEXT:    bgtz a3, .LBB0_2
+; RV32-NEXT:  # %bb.1:
+; RV32-NEXT:    mv a5, zero
+; RV32-NEXT:  .LBB0_2:
+; RV32-NEXT:    srai a4, a4, 24
+; RV32-NEXT:    andi a5, a5, 255
+; RV32-NEXT:    bgtz a6, .LBB0_4
+; RV32-NEXT:  # %bb.3:
+; RV32-NEXT:    mv a2, zero
+; RV32-NEXT:    j .LBB0_5
+; RV32-NEXT:  .LBB0_4:
+; RV32-NEXT:    srli a2, a2, 8
+; RV32-NEXT:  .LBB0_5:
+; RV32-NEXT:    slli a2, a2, 8
+; RV32-NEXT:    or a2, a5, a2
+; RV32-NEXT:    bgtz a4, .LBB0_7
+; RV32-NEXT:  # %bb.6:
+; RV32-NEXT:    mv a0, zero
+; RV32-NEXT:    j .LBB0_8
+; RV32-NEXT:  .LBB0_7:
+; RV32-NEXT:    srli a0, a0, 16
+; RV32-NEXT:  .LBB0_8:
+; RV32-NEXT:    sb a0, 2(a1)
+; RV32-NEXT:    sh a2, 0(a1)
+; RV32-NEXT:    ret
+;
+; RV64-LABEL: vec3_setcc_crash:
+; RV64:       # %bb.0:
+; RV64-NEXT:    lwu a0, 0(a0)
+; RV64-NEXT:    lui a2, 16
+; RV64-NEXT:    addiw a2, a2, -256
+; RV64-NEXT:    and a2, a0, a2
+; RV64-NEXT:    slli a3, a2, 48
+; RV64-NEXT:    srai a6, a3, 56
+; RV64-NEXT:    slli a4, a0, 56
+; RV64-NEXT:    srai a3, a4, 56
+; RV64-NEXT:    slli a4, a0, 40
+; RV64-NEXT:    mv a5, a0
+; RV64-NEXT:    bgtz a3, .LBB0_2
+; RV64-NEXT:  # %bb.1:
+; RV64-NEXT:    mv a5, zero
+; RV64-NEXT:  .LBB0_2:
+; RV64-NEXT:    srai a4, a4, 56
+; RV64-NEXT:    andi a5, a5, 255
+; RV64-NEXT:    bgtz a6, .LBB0_4
+; RV64-NEXT:  # %bb.3:
+; RV64-NEXT:    mv a2, zero
+; RV64-NEXT:    j .LBB0_5
+; RV64-NEXT:  .LBB0_4:
+; RV64-NEXT:    srli a2, a2, 8
+; RV64-NEXT:  .LBB0_5:
+; RV64-NEXT:    slli a2, a2, 8
+; RV64-NEXT:    or a2, a5, a2
+; RV64-NEXT:    bgtz a4, .LBB0_7
+; RV64-NEXT:  # %bb.6:
+; RV64-NEXT:    mv a0, zero
+; RV64-NEXT:    j .LBB0_8
+; RV64-NEXT:  .LBB0_7:
+; RV64-NEXT:    srli a0, a0, 16
+; RV64-NEXT:  .LBB0_8:
+; RV64-NEXT:    sb a0, 2(a1)
+; RV64-NEXT:    sh a2, 0(a1)
+; RV64-NEXT:    ret
+  %a = load <3 x i8>, <3 x i8>* %in
+  %cmp = icmp sgt <3 x i8> %a, zeroinitializer
+  %c = select <3 x i1> %cmp, <3 x i8> %a, <3 x i8> zeroinitializer
+  store <3 x i8> %c, <3 x i8>* %out
+  ret void
+}