[InstCombine][SVE] Skip scalable type for InstCombiner::getFlippedStrictnessPredicateAndConstant.

[huihuiz]

Summary

We cannot iterate on scalable vector, the number of elements is unknown at compile-time.

[huihuiz]

Current upstream crash with test attached.

[efriedma]

LGTM

We could add support for splats here, but not that important for now.

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

auto ConstantIsOk = [WillIncrement, IsSigned](ConstantInt *C) {
     return WillIncrement ? !C->isMaxValue(IsSigned) : !C->isMinValue(IsSigned);
   };
 
   Constant *SafeReplacementConstant = nullptr;
   if (auto *CI = dyn_cast<ConstantInt>(C)) {
     // Bail out if the constant can't be safely incremented/decremented.
     if (!ConstantIsOk(CI))
       return llvm::None;
-  } else if (auto *VTy = dyn_cast<VectorType>(Type)) {
-    unsigned NumElts = cast<FixedVectorType>(VTy)->getNumElements();
+  } else if (auto *FVTy = dyn_cast<FixedVectorType>(Type)) {
+    unsigned NumElts = FVTy->getNumElements();
     for (unsigned i = 0; i != NumElts; ++i) {
       Constant *Elt = C->getAggregateElement(i);
       if (!Elt)
         return llvm::None;
 
       if (isa<UndefValue>(Elt))
         continue;
 

llvm/test/Transforms/InstCombine/vscale_cmp.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+define <vscale x 2 x i1> @sge(<vscale x 2 x i8> %x) {
+; CHECK-LABEL: @sge(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sge <vscale x 2 x i8> [[X:%.*]], zeroinitializer
+; CHECK-NEXT:    ret <vscale x 2 x i1> [[CMP]]
+;
+  %cmp = icmp sge <vscale x 2 x i8> %x, zeroinitializer
+  ret <vscale x 2 x i1> %cmp
+}