Index: include/llvm/ADT/IntervalMap.h
===================================================================
--- include/llvm/ADT/IntervalMap.h
+++ include/llvm/ADT/IntervalMap.h
@@ -1040,8 +1040,17 @@
 
 public:
   explicit IntervalMap(Allocator &a) : height(0), rootSize(0), allocator(a) {
+#if defined(_MSC_VER) && !defined(_WIN64)
+    // x86 MSVC doesn't apply automatically (without `__declspec(align(...))`)
+    // alignments more than 4 bytes, even if `alignof` has returned so.
+    // The explanation:
+    // https://docs.microsoft.com/en-us/cpp/build/conflicts-with-the-x86-compiler
+    assert((uintptr_t(data.buffer) & (alignof(RootLeaf) - 1) & 3) == 0 &&
+           "Insufficient alignment");
+#else
     assert((uintptr_t(data.buffer) & (alignof(RootLeaf) - 1)) == 0 &&
            "Insufficient alignment");
+#endif
     new(&rootLeaf()) RootLeaf();
   }