Index: llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
===================================================================
--- llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -876,7 +876,9 @@
 Value *LibCallSimplifier::optimizeMemChr(CallInst *CI, IRBuilderBase &B) {
   Value *SrcStr = CI->getArgOperand(0);
   Value *Size = CI->getArgOperand(2);
-  annotateNonNullAndDereferenceable(CI, 0, Size, DL);
+  if (isKnownNonZero(Size, DL))
+    annotateNonNullNoUndefBasedOnAccess(CI, 0);
+
   Value *CharVal = CI->getArgOperand(1);
   ConstantInt *CharC = dyn_cast<ConstantInt>(CharVal);
   ConstantInt *LenC = dyn_cast<ConstantInt>(Size);
Index: llvm/test/Transforms/InstCombine/mem-deref-bytes.ll
===================================================================
--- llvm/test/Transforms/InstCombine/mem-deref-bytes.ll
+++ llvm/test/Transforms/InstCombine/mem-deref-bytes.ll
@@ -102,7 +102,7 @@
 
 define i8* @memcpy_const_size_set_deref(i8* nocapture readonly %d, i8* nocapture readonly %s) {
 ; CHECK-LABEL: @memcpy_const_size_set_deref(
-; CHECK-NEXT:    call void @llvm.memcpy.p0i8.p0i8.i64(i8* noundef nonnull align 1 dereferenceable(64) [[D:%.*]], i8* noundef nonnull align 1 dereferenceable(64) [[S:%.*]], i64 64, i1 false)
+; CHECK-NEXT:    tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* noundef nonnull align 1 dereferenceable(64) [[D:%.*]], i8* noundef nonnull align 1 dereferenceable(64) [[S:%.*]], i64 64, i1 false)
 ; CHECK-NEXT:    ret i8* [[D]]
 ;
   %call = tail call i8* @memcpy(i8* %d, i8* %s, i64 64)
@@ -111,7 +111,7 @@
 
 define i8* @memmove_const_size_set_deref(i8* nocapture readonly %d, i8* nocapture readonly %s) {
 ; CHECK-LABEL: @memmove_const_size_set_deref(
-; CHECK-NEXT:    call void @llvm.memmove.p0i8.p0i8.i64(i8* noundef nonnull align 1 dereferenceable(64) [[D:%.*]], i8* noundef nonnull align 1 dereferenceable(64) [[S:%.*]], i64 64, i1 false)
+; CHECK-NEXT:    tail call void @llvm.memmove.p0i8.p0i8.i64(i8* noundef nonnull align 1 dereferenceable(64) [[D:%.*]], i8* noundef nonnull align 1 dereferenceable(64) [[S:%.*]], i64 64, i1 false)
 ; CHECK-NEXT:    ret i8* [[D]]
 ;
   %call = tail call i8* @memmove(i8* %d, i8* %s, i64 64)
@@ -120,7 +120,7 @@
 
 define i8* @memset_const_size_set_deref(i8* nocapture readonly %s, i8 %c) {
 ; CHECK-LABEL: @memset_const_size_set_deref(
-; CHECK-NEXT:    call void @llvm.memset.p0i8.i64(i8* noundef nonnull align 1 dereferenceable(64) [[S:%.*]], i8 [[C:%.*]], i64 64, i1 false)
+; CHECK-NEXT:    tail call void @llvm.memset.p0i8.i64(i8* noundef nonnull align 1 dereferenceable(64) [[S:%.*]], i8 [[C:%.*]], i64 64, i1 false)
 ; CHECK-NEXT:    ret i8* [[S]]
 ;
   %call = tail call i8* @memset(i8* %s, i8 %c, i64 64)
@@ -129,7 +129,7 @@
 
 define i8* @memchr_const_size_set_deref(i8* nocapture readonly %s, i32 %c) {
 ; CHECK-LABEL: @memchr_const_size_set_deref(
-; CHECK-NEXT:    [[CALL:%.*]] = tail call i8* @memchr(i8* noundef nonnull dereferenceable(64) [[S:%.*]], i32 [[C:%.*]], i64 64)
+; CHECK-NEXT:    [[CALL:%.*]] = tail call i8* @memchr(i8* noundef nonnull dereferenceable(1) [[S:%.*]], i32 [[C:%.*]], i64 64)
 ; CHECK-NEXT:    ret i8* [[CALL]]
 ;
   %call = tail call i8* @memchr(i8* %s, i32 %c, i64 64)
Index: llvm/test/Transforms/InstCombine/memchr.ll
===================================================================
--- llvm/test/Transforms/InstCombine/memchr.ll
+++ llvm/test/Transforms/InstCombine/memchr.ll
@@ -50,7 +50,7 @@
 
 define void @test4(i32 %chr) {
 ; CHECK-LABEL: @test4(
-; CHECK-NEXT:    [[DST:%.*]] = call i8* @memchr(i8* noundef nonnull dereferenceable(14) getelementptr inbounds ([14 x i8], [14 x i8]* @hello, i32 0, i32 0), i32 [[CHR:%.*]], i32 14)
+; CHECK-NEXT:    [[DST:%.*]] = call i8* @memchr(i8* noundef nonnull dereferenceable(1) getelementptr inbounds ([14 x i8], [14 x i8]* @hello, i32 0, i32 0), i32 [[CHR:%.*]], i32 14)
 ; CHECK-NEXT:    store i8* [[DST]], i8** @chp, align 4
 ; CHECK-NEXT:    ret void
 ;
@@ -148,7 +148,7 @@
 ; No 64 bits here
 define i1 @test12(i32 %C) {
 ; CHECK-LABEL: @test12(
-; CHECK-NEXT:    [[DST:%.*]] = call i8* @memchr(i8* noundef nonnull dereferenceable(3) getelementptr inbounds ([4 x i8], [4 x i8]* @spaces, i32 0, i32 0), i32 [[C:%.*]], i32 3)
+; CHECK-NEXT:    [[DST:%.*]] = call i8* @memchr(i8* noundef nonnull dereferenceable(1) getelementptr inbounds ([4 x i8], [4 x i8]* @spaces, i32 0, i32 0), i32 [[C:%.*]], i32 3)
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i8* [[DST]], null
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
@@ -185,7 +185,7 @@
 
 define i1 @test15(i32 %C) {
 ; CHECK-LABEL: @test15(
-; CHECK-NEXT:    [[DST:%.*]] = call i8* @memchr(i8* noundef nonnull dereferenceable(3) getelementptr inbounds ([3 x i8], [3 x i8]* @negative, i32 0, i32 0), i32 [[C:%.*]], i32 3)
+; CHECK-NEXT:    [[DST:%.*]] = call i8* @memchr(i8* noundef nonnull dereferenceable(1) getelementptr inbounds ([3 x i8], [3 x i8]* @negative, i32 0, i32 0), i32 [[C:%.*]], i32 3)
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i8* [[DST]], null
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
@@ -225,7 +225,7 @@
 
 define i8* @test18(i8* %str, i32 %c) {
 ; CHECK-LABEL: @test18(
-; CHECK-NEXT:    [[RET:%.*]] = call i8* @memchr(i8* noundef nonnull dereferenceable(5) [[STR:%.*]], i32 [[C:%.*]], i32 5)
+; CHECK-NEXT:    [[RET:%.*]] = call i8* @memchr(i8* noundef nonnull dereferenceable(1) [[STR:%.*]], i32 [[C:%.*]], i32 5)
 ; CHECK-NEXT:    ret i8* [[RET]]
 ;
 
@@ -235,7 +235,7 @@
 
 define i8* @test19(i8* %str, i32 %c) null_pointer_is_valid {
 ; CHECK-LABEL: @test19(
-; CHECK-NEXT:    [[RET:%.*]] = call i8* @memchr(i8* noundef dereferenceable(5) [[STR:%.*]], i32 [[C:%.*]], i32 5)
+; CHECK-NEXT:    [[RET:%.*]] = call i8* @memchr(i8* noundef [[STR:%.*]], i32 [[C:%.*]], i32 5)
 ; CHECK-NEXT:    ret i8* [[RET]]
 ;
 
Index: llvm/test/Transforms/InstCombine/strchr-1.ll
===================================================================
--- llvm/test/Transforms/InstCombine/strchr-1.ll
+++ llvm/test/Transforms/InstCombine/strchr-1.ll
@@ -49,7 +49,7 @@
 
 define void @test_simplify4(i32 %chr) {
 ; CHECK-LABEL: @test_simplify4(
-; CHECK-NEXT:    [[MEMCHR:%.*]] = call i8* @memchr(i8* noundef nonnull dereferenceable(14) getelementptr inbounds ([14 x i8], [14 x i8]* @hello, i32 0, i32 0), i32 [[CHR:%.*]], i32 14)
+; CHECK-NEXT:    [[MEMCHR:%.*]] = call i8* @memchr(i8* noundef nonnull dereferenceable(1) getelementptr inbounds ([14 x i8], [14 x i8]* @hello, i32 0, i32 0), i32 [[CHR:%.*]], i32 14)
 ; CHECK-NEXT:    store i8* [[MEMCHR]], i8** @chp, align 4
 ; CHECK-NEXT:    ret void
 ;