[SROA] prevent crash on large memset length (PR50910)

I don't know much about this pass, but we need a stronger
check on the memset length arg to avoid an assert. The
current code was added with D59000.
The test is reduced from:
https://llvm.org/PR50910

Differential Revision: https://reviews.llvm.org/D106462

llvm/lib/Transforms/Scalar/SROA.cpp

@@ -2811,10 +2811,11 @@ class llvm::sroa::AllocaSliceRewriter
  if (BeginOffset > NewAllocaBeginOffset ||
  EndOffset < NewAllocaEndOffset)
  return false;
+ // Length must be in range for FixedVectorType.
  auto *C = cast<ConstantInt>(II.getLength());
- if (C->getBitWidth() > 64)
+ const uint64_t Len = C->getLimitedValue();
+ if (Len > std::numeric_limits<unsigned>::max())
  return false;
- const auto Len = C->getZExtValue();
  auto *Int8Ty = IntegerType::getInt8Ty(NewAI.getContext());
  auto *SrcTy = FixedVectorType::get(Int8Ty, Len);
  return canConvertValue(DL, SrcTy, AllocaTy) &&

llvm/test/Transforms/SROA/slice-width.ll

@@ -145,3 +145,16 @@ define void @PR50888() {
  call void @llvm.memset.p0i8.i64(i8* align 16 %array, i8 0, i64 ptrtoint (void ()* @PR50888 to i64), i1 false)
  ret void
 }
+
+; Don't crash on out-of-bounds length.
+
+define void @PR50910() {
+; CHECK-LABEL: @PR50910(
+; CHECK-NEXT: [[T1:%.*]] = alloca i8, i64 1, align 8
+; CHECK-NEXT: call void @llvm.memset.p0i8.i64(i8* align 8 [[T1]], i8 0, i64 1, i1 false)
+; CHECK-NEXT: ret void
+;
+ %t1 = alloca i8, i64 1, align 8
+ call void @llvm.memset.p0i8.i64(i8* align 8 %t1, i8 0, i64 4294967296, i1 false)
+ ret void
+}