diff --git a/llvm/lib/Transforms/Vectorize/VectorCombine.cpp b/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
--- a/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
+++ b/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
@@ -687,6 +687,11 @@
   if (!TTI.getNumberOfRegisters(TTI.getRegisterClassForType(/*Vector*/ true)))
     return false;
 
+  // Do not vectorize scalar load under asan or tsan. The widened load may
+  // overlap bytes marked as __asan_poison_memory_region or bytes being
+  // concurrently modified.
+  bool CanWiden = !F.hasFnAttribute(Attribute::SanitizeAddress) &&
+                  !F.hasFnAttribute(Attribute::SanitizeThread);
   bool MadeChange = false;
   for (BasicBlock &BB : F) {
     // Ignore unreachable basic blocks.
@@ -700,7 +705,8 @@
       if (isa<DbgInfoIntrinsic>(I))
         continue;
       Builder.SetInsertPoint(&I);
-      MadeChange |= vectorizeLoadInsert(I);
+      if (CanWiden)
+        MadeChange |= vectorizeLoadInsert(I);
       MadeChange |= foldExtractExtract(I);
       MadeChange |= foldBitcastShuf(I);
       MadeChange |= scalarizeBinopOrCmp(I);
diff --git a/llvm/test/Transforms/VectorCombine/X86/load.ll b/llvm/test/Transforms/VectorCombine/X86/load.ll
--- a/llvm/test/Transforms/VectorCombine/X86/load.ll
+++ b/llvm/test/Transforms/VectorCombine/X86/load.ll
@@ -292,6 +292,38 @@
   ret <8 x i16> %r
 }
 
+; Negative test - disable under asan because widened load can cause spurious
+; use-after-poison issues when __asan_poison_memory_region is used.
+
+define <8 x i16> @gep10_load_i16_insert_v8i16_asan(<8 x i16>* align 16 dereferenceable(32) %p) sanitize_address {
+; CHECK-LABEL: @gep10_load_i16_insert_v8i16_asan(
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds <8 x i16>, <8 x i16>* [[P:%.*]], i64 1, i64 0
+; CHECK-NEXT:    [[S:%.*]] = load i16, i16* [[GEP]], align 16
+; CHECK-NEXT:    [[R:%.*]] = insertelement <8 x i16> undef, i16 [[S]], i64 0
+; CHECK-NEXT:    ret <8 x i16> [[R]]
+;
+  %gep = getelementptr inbounds <8 x i16>, <8 x i16>* %p, i64 1, i64 0
+  %s = load i16, i16* %gep, align 16
+  %r = insertelement <8 x i16> undef, i16 %s, i64 0
+  ret <8 x i16> %r
+}
+
+; Negative test - disable under tsan because widened load may overlap bytes
+; being concurrently modified. tsan does not know that some bytes are undef.
+
+define <8 x i16> @gep10_load_i16_insert_v8i16_tsan(<8 x i16>* align 16 dereferenceable(32) %p) sanitize_thread {
+; CHECK-LABEL: @gep10_load_i16_insert_v8i16_tsan(
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds <8 x i16>, <8 x i16>* [[P:%.*]], i64 1, i64 0
+; CHECK-NEXT:    [[S:%.*]] = load i16, i16* [[GEP]], align 16
+; CHECK-NEXT:    [[R:%.*]] = insertelement <8 x i16> undef, i16 [[S]], i64 0
+; CHECK-NEXT:    ret <8 x i16> [[R]]
+;
+  %gep = getelementptr inbounds <8 x i16>, <8 x i16>* %p, i64 1, i64 0
+  %s = load i16, i16* %gep, align 16
+  %r = insertelement <8 x i16> undef, i16 %s, i64 0
+  ret <8 x i16> %r
+}
+
 ; Negative test - can't safely load the offset vector, but could load+shuffle.
 
 define <8 x i16> @gep10_load_i16_insert_v8i16_deref(<8 x i16>* align 16 dereferenceable(31) %p) {