diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 13eae549b2ce4..254795ec24453 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -7395,11 +7395,34 @@ static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I, bool PtrValu
     // Look through GEPs. A load from a GEP derived from NULL is still undefined
     if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Use))
       if (GEP->getPointerOperand() == I) {
-        if (!GEP->isInBounds() || !GEP->hasAllZeroIndices())
+        // The current base address is null, there are four cases to consider:
+        // getelementptr (TY, null, 0)                 -> null
+        // getelementptr (TY, null, not zero)          -> may be modified
+        // getelementptr inbounds (TY, null, 0)        -> null
+        // getelementptr inbounds (TY, null, not zero) -> poison iff null is
+        // undefined?
+        if (!GEP->hasAllZeroIndices() &&
+            (!GEP->isInBounds() ||
+             NullPointerIsDefined(GEP->getFunction(),
+                                  GEP->getPointerAddressSpace())))
           PtrValueMayBeModified = true;
         return passingValueIsAlwaysUndefined(V, GEP, PtrValueMayBeModified);
       }
 
+    // Look through return.
+    if (ReturnInst *Ret = dyn_cast<ReturnInst>(Use)) {
+      bool HasNoUndefAttr =
+          Ret->getFunction()->hasRetAttribute(Attribute::NoUndef);
+      // Return undefined to a noundef return value is undefined.
+      if (isa<UndefValue>(C) && HasNoUndefAttr)
+        return true;
+      // Return null to a nonnull+noundef return value is undefined.
+      if (C->isNullValue() && HasNoUndefAttr &&
+          Ret->getFunction()->hasRetAttribute(Attribute::NonNull)) {
+        return !PtrValueMayBeModified;
+      }
+    }
+
     // Look through bitcasts.
     if (BitCastInst *BC = dyn_cast<BitCastInst>(Use))
       return passingValueIsAlwaysUndefined(V, BC, PtrValueMayBeModified);
diff --git a/llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll b/llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll
index 5ba43c055f9be..757340527ec03 100644
--- a/llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll
+++ b/llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll
@@ -444,6 +444,28 @@ else:
 define void @test9_gep_inbounds_nonzero(i1 %X, ptr %Y) {
 ; CHECK-LABEL: @test9_gep_inbounds_nonzero(
 ; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = xor i1 [[X:%.*]], true
+; CHECK-NEXT:    call void @llvm.assume(i1 [[TMP0]])
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i8, ptr [[Y:%.*]], i64 12
+; CHECK-NEXT:    [[TMP1:%.*]] = call ptr @fn_nonnull_noundef_arg(ptr [[GEP]])
+; CHECK-NEXT:    ret void
+;
+entry:
+  br i1 %X, label %if, label %else
+
+if:
+  br label %else
+
+else:
+  %phi = phi ptr [ %Y, %entry ], [ null, %if ]
+  %gep = getelementptr inbounds i8, ptr %phi, i64 12
+  call ptr @fn_nonnull_noundef_arg(ptr %gep)
+  ret void
+}
+
+define void @test9_gep_inbounds_nonzero_null_defined(i1 %X, ptr %Y) #0 {
+; CHECK-LABEL: @test9_gep_inbounds_nonzero_null_defined(
+; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = select i1 [[X:%.*]], ptr null, ptr [[Y:%.*]]
 ; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i8, ptr [[SPEC_SELECT]], i64 12
 ; CHECK-NEXT:    [[TMP0:%.*]] = call ptr @fn_nonnull_noundef_arg(ptr [[GEP]])
@@ -462,9 +484,30 @@ else:
   ret void
 }
 
+define void @test9_gep_inbounds_unknown_null(i1 %X, ptr %Y, i64 %I) {
+; CHECK-LABEL: @test9_gep_inbounds_unknown_null(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = xor i1 [[X:%.*]], true
+; CHECK-NEXT:    call void @llvm.assume(i1 [[TMP0]])
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i8, ptr [[Y:%.*]], i64 [[I:%.*]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call ptr @fn_nonnull_noundef_arg(ptr [[GEP]])
+; CHECK-NEXT:    ret void
+;
+entry:
+  br i1 %X, label %if, label %else
+
+if:
+  br label %else
+
+else:
+  %phi = phi ptr [ %Y, %entry ], [ null, %if ]
+  %gep = getelementptr inbounds i8, ptr %phi, i64 %I
+  call ptr @fn_nonnull_noundef_arg(ptr %gep)
+  ret void
+}
 
-define void @test9_gep_inbouds_unknown_null(i1 %X, ptr %Y, i64 %I) {
-; CHECK-LABEL: @test9_gep_inbouds_unknown_null(
+define void @test9_gep_inbounds_unknown_null_defined(i1 %X, ptr %Y, i64 %I) #0 {
+; CHECK-LABEL: @test9_gep_inbounds_unknown_null_defined(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = select i1 [[X:%.*]], ptr null, ptr [[Y:%.*]]
 ; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i8, ptr [[SPEC_SELECT]], i64 [[I:%.*]]
@@ -484,6 +527,27 @@ else:
   ret void
 }
 
+define void @test9_gep_inbounds_unknown_null_call_noundef(i1 %X, ptr %Y, i64 %I) {
+; CHECK-LABEL: @test9_gep_inbounds_unknown_null_call_noundef(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = select i1 [[X:%.*]], ptr null, ptr [[Y:%.*]]
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i8, ptr [[SPEC_SELECT]], i64 [[I:%.*]]
+; CHECK-NEXT:    [[TMP0:%.*]] = call ptr @fn_noundef_arg(ptr [[GEP]])
+; CHECK-NEXT:    ret void
+;
+entry:
+  br i1 %X, label %if, label %else
+
+if:
+  br label %else
+
+else:
+  %phi = phi ptr [ %Y, %entry ], [ null, %if ]
+  %gep = getelementptr inbounds i8, ptr %phi, i64 %I
+  call ptr @fn_noundef_arg(ptr %gep)
+  ret void
+}
+
 define void @test9_gep_unknown_null(i1 %X, ptr %Y, i64 %I) {
 ; CHECK-LABEL: @test9_gep_unknown_null(
 ; CHECK-NEXT:  entry:
diff --git a/llvm/test/Transforms/SimplifyCFG/unreachable-eliminate-on-ret.ll b/llvm/test/Transforms/SimplifyCFG/unreachable-eliminate-on-ret.ll
new file mode 100644
index 0000000000000..924f98a46ab54
--- /dev/null
+++ b/llvm/test/Transforms/SimplifyCFG/unreachable-eliminate-on-ret.ll
@@ -0,0 +1,141 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -passes=simplifycfg -simplifycfg-require-and-preserve-domtree=1 -S < %s | FileCheck %s
+
+define noundef i32 @test_ret_noundef(i1 %cond) {
+; CHECK-LABEL: @test_ret_noundef(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    ret i32 1
+;
+entry:
+  br i1 %cond, label %bb1, label %bb2
+
+bb1:
+  br label %bb2
+
+bb2:
+  %r = phi i32 [ undef, %entry ], [ 1, %bb1 ]
+  ret i32 %r
+}
+
+define i32 @test_ret(i1 %cond) {
+; CHECK-LABEL: @test_ret(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = select i1 [[COND:%.*]], i32 1, i32 undef
+; CHECK-NEXT:    ret i32 [[SPEC_SELECT]]
+;
+entry:
+  br i1 %cond, label %bb1, label %bb2
+
+bb1:
+  br label %bb2
+
+bb2:
+  %r = phi i32 [ undef, %entry ], [ 1, %bb1 ]
+  ret i32 %r
+}
+
+define nonnull noundef ptr @test_ret_ptr_nonnull_noundef(i1 %cond, ptr %x) {
+; CHECK-LABEL: @test_ret_ptr_nonnull_noundef(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    call void @llvm.assume(i1 [[COND:%.*]])
+; CHECK-NEXT:    ret ptr [[X:%.*]]
+;
+entry:
+  br i1 %cond, label %bb1, label %bb2
+
+bb1:
+  br label %bb2
+
+bb2:
+  %r = phi ptr [ null, %entry ], [ %x, %bb1 ]
+  ret ptr %r
+}
+
+define nonnull noundef ptr @test_ret_ptr_nonnull_noundef_gep_nonzero(i1 %cond, ptr %x) {
+; CHECK-LABEL: @test_ret_ptr_nonnull_noundef_gep_nonzero(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = select i1 [[COND:%.*]], ptr [[X:%.*]], ptr null
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr ptr, ptr [[SPEC_SELECT]], i64 12
+; CHECK-NEXT:    ret ptr [[GEP]]
+;
+entry:
+  br i1 %cond, label %bb1, label %bb2
+
+bb1:
+  br label %bb2
+
+bb2:
+  %phi = phi ptr [ null, %entry ], [ %x, %bb1 ]
+  %gep = getelementptr ptr, ptr %phi, i64 12
+  ret ptr %gep
+}
+
+define nonnull noundef ptr @test_ret_ptr_nonnull_noundef_gep_inbounds_nonzero(i1 %cond, ptr %x) {
+; CHECK-LABEL: @test_ret_ptr_nonnull_noundef_gep_inbounds_nonzero(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    call void @llvm.assume(i1 [[COND:%.*]])
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds ptr, ptr [[X:%.*]], i64 12
+; CHECK-NEXT:    ret ptr [[GEP]]
+;
+entry:
+  br i1 %cond, label %bb1, label %bb2
+
+bb1:
+  br label %bb2
+
+bb2:
+  %phi = phi ptr [ null, %entry ], [ %x, %bb1 ]
+  %gep = getelementptr inbounds ptr, ptr %phi, i64 12
+  ret ptr %gep
+}
+
+define nonnull ptr @test_ret_ptr_nonnull(i1 %cond, ptr %x) {
+; CHECK-LABEL: @test_ret_ptr_nonnull(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = select i1 [[COND:%.*]], ptr [[X:%.*]], ptr null
+; CHECK-NEXT:    ret ptr [[SPEC_SELECT]]
+;
+entry:
+  br i1 %cond, label %bb1, label %bb2
+
+bb1:
+  br label %bb2
+
+bb2:
+  %r = phi ptr [ null, %entry ], [ %x, %bb1 ]
+  ret ptr %r
+}
+
+define noundef ptr @test_ret_ptr_noundef(i1 %cond, ptr %x) {
+; CHECK-LABEL: @test_ret_ptr_noundef(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = select i1 [[COND:%.*]], ptr [[X:%.*]], ptr null
+; CHECK-NEXT:    ret ptr [[SPEC_SELECT]]
+;
+entry:
+  br i1 %cond, label %bb1, label %bb2
+
+bb1:
+  br label %bb2
+
+bb2:
+  %r = phi ptr [ null, %entry ], [ %x, %bb1 ]
+  ret ptr %r
+}
+
+define ptr @test_ret_ptr(i1 %cond, ptr %x) {
+; CHECK-LABEL: @test_ret_ptr(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = select i1 [[COND:%.*]], ptr [[X:%.*]], ptr null
+; CHECK-NEXT:    ret ptr [[SPEC_SELECT]]
+;
+entry:
+  br i1 %cond, label %bb1, label %bb2
+
+bb1:
+  br label %bb2
+
+bb2:
+  %r = phi ptr [ null, %entry ], [ %x, %bb1 ]
+  ret ptr %r
+}