Index: llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
+++ llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
@@ -1702,10 +1702,18 @@
       auto &Context = Call->getContext();
       auto &DL = Call->getModule()->getDataLayout();
       auto GetBaseAndOffset = [&](Value *Derived) {
-        assert(PointerToBase.count(Derived));
+        Value *Base = nullptr;
+        // Optimizations in unreachable code might substitute the real pointer
+        // with undef, poison or null-derived constant.
+        if (isa<Constant>(Derived))
+          Base =
+              ConstantPointerNull::get(cast<PointerType>(Derived->getType()));
+        else {
+          assert(PointerToBase.count(Derived));
+          Base = PointerToBase.find(Derived)->second;
+        }
         unsigned AddressSpace = Derived->getType()->getPointerAddressSpace();
         unsigned IntPtrSize = DL.getPointerSizeInBits(AddressSpace);
-        Value *Base = PointerToBase.find(Derived)->second;
         Value *Base_int = Builder.CreatePtrToInt(
             Base, Type::getIntNTy(Context, IntPtrSize));
         Value *Derived_int = Builder.CreatePtrToInt(
Index: llvm/test/Transforms/RewriteStatepointsForGC/pr56493.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/RewriteStatepointsForGC/pr56493.ll
@@ -0,0 +1,18 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -passes=rewrite-statepoints-for-gc -S < %s | FileCheck %s
+
+; Make sure this doesn't crash.
+define void @test() gc "statepoint-example" personality i32* ()* @zot {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    [[STATEPOINT_TOKEN:%.*]] = call token (i64, i32, void (i32 addrspace(1)*, i64, i32 addrspace(1)*, i64, i64)*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_isVoidp1i32i64p1i32i64i64f(i64 2882400000, i32 0, void (i32 addrspace(1)*, i64, i32 addrspace(1)*, i64, i64)* elementtype(void (i32 addrspace(1)*, i64, i32 addrspace(1)*, i64, i64)) @__llvm_memcpy_element_unordered_atomic_safepoint_4, i32 5, i32 0, i32 addrspace(1)* null, i64 undef, i32 addrspace(1)* null, i64 ptrtoint (i8 addrspace(1)* getelementptr inbounds (i8, i8 addrspace(1)* null, i64 16) to i64), i64 undef, i32 0, i32 0) [ "deopt"() ]
+; CHECK-NEXT:    ret void
+;
+bb:
+  call void @llvm.memcpy.element.unordered.atomic.p1i32.p1i32.i64(i32 addrspace(1)* elementtype(i32) align 8 undef, i32 addrspace(1)* elementtype(i32) align 16 bitcast (i8 addrspace(1)* getelementptr inbounds (i8, i8 addrspace(1)* null, i64 16) to i32 addrspace(1)*), i64 undef, i32 4) #3 [ "deopt"() ]
+  ret void
+}
+
+declare i32* @zot()
+
+declare void @llvm.memcpy.element.unordered.atomic.p1i32.p1i32.i64(i32 addrspace(1)* nocapture writeonly, i32 addrspace(1)* nocapture readonly, i64, i32 immarg)