Index: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -2730,8 +2730,20 @@
   if (!MemRuntimeCheck)
     return;
 
-  assert(!BB->getParent()->hasOptSize() &&
-         "Cannot emit memory checks when optimizing for size");
+  if (BB->getParent()->hasOptSize()) {
+    bool Forced = Cost->Hints->getForce() == LoopVectorizeHints::FK_Enabled;
+    assert(Forced && "Cannot emit memory checks when optimizing for size, "
+                     "unless forced to vectorize.");
+    if (Forced)
+      ORE->emit([&]() {
+        return OptimizationRemarkAnalysis(DEBUG_TYPE, "VectorizationCodeSize",
+                                          L->getStartLoc(), L->getHeader())
+               << "Code-size may be reduced by removing forced "
+                  "vectorization, or by source-code modifications "
+                  "eliminating the need for runtime checks "
+                  "(e.g., adding 'restrict').";
+      });
+  }
 
   // Create a new block containing the memory check.
   BB->setName("vector.memcheck");
Index: llvm/test/Transforms/LoopVectorize/runtime-check.ll
===================================================================
--- llvm/test/Transforms/LoopVectorize/runtime-check.ll
+++ llvm/test/Transforms/LoopVectorize/runtime-check.ll
@@ -1,5 +1,6 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
-; RUN: opt < %s  -loop-vectorize -force-vector-interleave=1 -force-vector-width=4 -dce -instcombine -S | FileCheck %s
+; RUN: opt < %s -loop-vectorize -force-vector-interleave=1 -force-vector-width=4 -dce -instcombine -S | FileCheck %s
+; RUN: opt < %s -loop-vectorize -disable-basicaa -S -pass-remarks-analysis='loop-vectorize' 2>&1 | FileCheck %s -check-prefix=FORCED_OPTSIZE
 
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
 
@@ -157,6 +158,30 @@
   ret void
 }
 
+define dso_local void @forced_optsize(i64* noalias nocapture readonly %x_p, i64* noalias nocapture readonly %y_p, i64* noalias nocapture %z_p) local_unnamed_addr #0 {
+; FORCED_OPTSIZE-LABEL: @forced_optsize(
+; FORCED_OPTSIZE:       vector.body:
+entry:
+  br label %for.body
+
+for.cond.cleanup:
+  ret void
+
+for.body:
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %arrayidx = getelementptr inbounds i64, i64* %x_p, i64 %indvars.iv
+  %0 = load i64, i64* %arrayidx, align 8
+  %arrayidx2 = getelementptr inbounds i64, i64* %y_p, i64 %indvars.iv
+  %1 = load i64, i64* %arrayidx2, align 8
+  %add = add nsw i64 %1, %0
+  %arrayidx4 = getelementptr inbounds i64, i64* %z_p, i64 %indvars.iv
+  store i64 %add, i64* %arrayidx4, align 8
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond = icmp eq i64 %indvars.iv.next, 128
+  br i1 %exitcond, label %for.cond.cleanup, label %for.body, !llvm.loop !12
+}
+
+
 ; CHECK: !9 = !DILocation(line: 101, column: 1, scope: !{{.*}})
 
 !llvm.module.flags = !{!0, !1}
@@ -177,3 +202,6 @@
                              splitDebugFilename: "abc.debug", emissionKind: 2)
 !10 = !DIFile(filename: "path/to/file", directory: "/path/to/dir")
 !11 = !{i32 2, !"Debug Info Version", i32 3}
+!12 = distinct !{!12, !13, !14}
+!13 = !{!"llvm.loop.vectorize.width", i32 2}
+!14 = !{!"llvm.loop.vectorize.enable", i1 true}