diff --git a/llvm/lib/Transforms/Utils/BuildLibCalls.cpp b/llvm/lib/Transforms/Utils/BuildLibCalls.cpp
--- a/llvm/lib/Transforms/Utils/BuildLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/BuildLibCalls.cpp
@@ -36,6 +36,7 @@
 STATISTIC(NumNoUnwind, "Number of functions inferred as nounwind");
 STATISTIC(NumNoCapture, "Number of arguments inferred as nocapture");
 STATISTIC(NumReadOnlyArg, "Number of arguments inferred as readonly");
+STATISTIC(NumWriteOnlyArg, "Number of arguments inferred as writeonly");
 STATISTIC(NumNoAlias, "Number of function returns inferred as noalias");
 STATISTIC(NumNoUndef, "Number of function returns inferred as noundef returns");
 STATISTIC(NumNonNull, "Number of function returns inferred as nonnull returns");
@@ -105,6 +106,14 @@
   return true;
 }
 
+static bool setOnlyWritesMemory(Function &F, unsigned ArgNo) {
+  if (F.hasParamAttribute(ArgNo, Attribute::WriteOnly))
+    return false;
+  F.addParamAttr(ArgNo, Attribute::WriteOnly);
+  ++NumWriteOnlyArg;
+  return true;
+}
+
 static bool setRetAndArgsNoUndef(Function &F) {
   bool Changed = false;
   if (!F.getReturnType()->isVoidTy() &&
@@ -203,9 +212,6 @@
     return Changed;
   case LibFunc_strcpy:
   case LibFunc_strncpy:
-    Changed |= setDoesNotAlias(F, 0);
-    Changed |= setDoesNotAlias(F, 1);
-    LLVM_FALLTHROUGH;
   case LibFunc_strcat:
   case LibFunc_strncat:
     Changed |= setReturnedArg(F, 0);
@@ -213,8 +219,12 @@
   case LibFunc_stpcpy:
   case LibFunc_stpncpy:
     Changed |= setDoesNotThrow(F);
+    Changed |= setDoesNotCapture(F, 0);
     Changed |= setDoesNotCapture(F, 1);
+    Changed |= setOnlyWritesMemory(F, 0);
     Changed |= setOnlyReadsMemory(F, 1);
+    Changed |= setDoesNotAlias(F, 0);
+    Changed |= setDoesNotAlias(F, 1);
     return Changed;
   case LibFunc_strxfrm:
     Changed |= setDoesNotThrow(F);
diff --git a/llvm/test/Transforms/InferFunctionAttrs/annotate.ll b/llvm/test/Transforms/InferFunctionAttrs/annotate.ll
--- a/llvm/test/Transforms/InferFunctionAttrs/annotate.ll
+++ b/llvm/test/Transforms/InferFunctionAttrs/annotate.ll
@@ -825,16 +825,16 @@
 ; CHECK-LINUX: declare noundef i32 @statvfs64(i8* nocapture noundef readonly, %opaque* nocapture noundef) [[G1]]
 declare i32 @statvfs64(i8*, %opaque*)
 
-; CHECK: declare i8* @stpcpy(i8*, i8* nocapture readonly) [[G1]]
+; CHECK: declare i8* @stpcpy(i8* noalias nocapture writeonly, i8* noalias nocapture readonly) [[G1]]
 declare i8* @stpcpy(i8*, i8*)
 
-; CHECK: declare i8* @stpncpy(i8*, i8* nocapture readonly, i64) [[G1]]
+; CHECK: declare i8* @stpncpy(i8* noalias nocapture writeonly, i8* noalias nocapture readonly, i64) [[G1]]
 declare i8* @stpncpy(i8*, i8*, i64)
 
 ; CHECK: declare i32 @strcasecmp(i8* nocapture, i8* nocapture) [[G2]]
 declare i32 @strcasecmp(i8*, i8*)
 
-; CHECK: declare i8* @strcat(i8* returned, i8* nocapture readonly) [[G1]]
+; CHECK: declare i8* @strcat(i8* noalias nocapture returned writeonly, i8* noalias nocapture readonly) [[G1]]
 declare i8* @strcat(i8*, i8*)
 
 ; CHECK: declare i8* @strchr(i8*, i32) [[ARGMEMONLY_NOFREE_NOUNWIND_READONLY]]
@@ -846,7 +846,7 @@
 ; CHECK: declare i32 @strcoll(i8* nocapture, i8* nocapture) [[G2]]
 declare i32 @strcoll(i8*, i8*)
 
-; CHECK: declare i8* @strcpy(i8* noalias returned, i8* noalias nocapture readonly) [[G1]]
+; CHECK: declare i8* @strcpy(i8* noalias nocapture returned writeonly, i8* noalias nocapture readonly) [[G1]]
 declare i8* @strcpy(i8*, i8*)
 
 ; CHECK: declare i64 @strcspn(i8* nocapture, i8* nocapture) [[ARGMEMONLY_NOFREE_NOUNWIND_READONLY]]
@@ -861,13 +861,13 @@
 ; CHECK: declare i32 @strncasecmp(i8* nocapture, i8* nocapture, i64) [[G2]]
 declare i32 @strncasecmp(i8*, i8*, i64)
 
-; CHECK: declare i8* @strncat(i8* returned, i8* nocapture readonly, i64) [[G1]]
+; CHECK: declare i8* @strncat(i8* noalias nocapture returned writeonly, i8* noalias nocapture readonly, i64) [[G1]]
 declare i8* @strncat(i8*, i8*, i64)
 
 ; CHECK: declare i32 @strncmp(i8* nocapture, i8* nocapture, i64) [[ARGMEMONLY_NOFREE_NOUNWIND_READONLY]]
 declare i32 @strncmp(i8*, i8*, i64)
 
-; CHECK: declare i8* @strncpy(i8* noalias returned, i8* noalias nocapture readonly, i64) [[G1]]
+; CHECK: declare i8* @strncpy(i8* noalias nocapture returned writeonly, i8* noalias nocapture readonly, i64) [[G1]]
 declare i8* @strncpy(i8*, i8*, i64)
 
 ; CHECK: declare noalias i8* @strndup(i8* nocapture readonly, i64) [[G1]]
diff --git a/llvm/test/Transforms/PhaseOrdering/dse-libcalls.ll b/llvm/test/Transforms/PhaseOrdering/dse-libcalls.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Transforms/PhaseOrdering/dse-libcalls.ll
@@ -0,0 +1,93 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -S -O2 | FileCheck %s --check-prefixes=CHECK,OLDPM
+; RUN: opt -passes='default<O2>' -S < %s | FileCheck %s --check-prefixes=CHECK,NEWPM
+
+
+declare i8* @strcpy(i8*, i8*)
+declare i8* @strncpy(i8*, i8*, i64)
+declare i8* @strcat(i8*, i8*)
+declare i8* @strncat(i8*, i8*, i64)
+
+define void @dse_strcpy(i8* nocapture readonly %src) {
+; OLDPM-LABEL: @dse_strcpy(
+; OLDPM-NEXT:    ret void
+;
+; NEWPM-LABEL: @dse_strcpy(
+; NEWPM-NEXT:    [[A:%.*]] = alloca [256 x i8], align 16
+; NEWPM-NEXT:    [[BUF:%.*]] = getelementptr inbounds [256 x i8], [256 x i8]* [[A]], i64 0, i64 0
+; NEWPM-NEXT:    call void @llvm.lifetime.start.p0i8(i64 256, i8* nonnull [[BUF]])
+; NEWPM-NEXT:    [[TMP1:%.*]] = call i8* @strcpy(i8* nonnull [[BUF]], i8* nonnull dereferenceable(1) [[SRC:%.*]])
+; NEWPM-NEXT:    call void @llvm.lifetime.end.p0i8(i64 256, i8* nonnull [[BUF]])
+; NEWPM-NEXT:    ret void
+;
+  %a = alloca [256 x i8], align 16
+  %buf = getelementptr inbounds [256 x i8], [256 x i8]* %a, i64 0, i64 0
+  call void @llvm.lifetime.start.p0i8(i64 256, i8* nonnull %buf)
+  call i8* @strcpy(i8* nonnull %buf, i8* nonnull dereferenceable(1) %src)
+  call void @llvm.lifetime.end.p0i8(i64 256, i8* nonnull %buf)
+  ret void
+}
+
+define void @dse_strncpy(i8* nocapture readonly %src) {
+; OLDPM-LABEL: @dse_strncpy(
+; OLDPM-NEXT:    ret void
+;
+; NEWPM-LABEL: @dse_strncpy(
+; NEWPM-NEXT:    [[A:%.*]] = alloca [256 x i8], align 16
+; NEWPM-NEXT:    [[BUF:%.*]] = getelementptr inbounds [256 x i8], [256 x i8]* [[A]], i64 0, i64 0
+; NEWPM-NEXT:    call void @llvm.lifetime.start.p0i8(i64 256, i8* nonnull [[BUF]])
+; NEWPM-NEXT:    [[TMP1:%.*]] = call i8* @strncpy(i8* nonnull [[BUF]], i8* nonnull dereferenceable(1) [[SRC:%.*]], i64 6)
+; NEWPM-NEXT:    call void @llvm.lifetime.end.p0i8(i64 256, i8* nonnull [[BUF]])
+; NEWPM-NEXT:    ret void
+;
+  %a = alloca [256 x i8], align 16
+  %buf = getelementptr inbounds [256 x i8], [256 x i8]* %a, i64 0, i64 0
+  call void @llvm.lifetime.start.p0i8(i64 256, i8* nonnull %buf)
+  call i8* @strncpy(i8* nonnull %buf, i8* nonnull dereferenceable(1) %src, i64 6)
+  call void @llvm.lifetime.end.p0i8(i64 256, i8* nonnull %buf)
+  ret void
+}
+
+define void @dse_strcat(i8* nocapture readonly %src) {
+; OLDPM-LABEL: @dse_strcat(
+; OLDPM-NEXT:    ret void
+;
+; NEWPM-LABEL: @dse_strcat(
+; NEWPM-NEXT:    [[A:%.*]] = alloca [256 x i8], align 16
+; NEWPM-NEXT:    [[BUF:%.*]] = getelementptr inbounds [256 x i8], [256 x i8]* [[A]], i64 0, i64 0
+; NEWPM-NEXT:    call void @llvm.lifetime.start.p0i8(i64 256, i8* nonnull [[BUF]])
+; NEWPM-NEXT:    [[TMP1:%.*]] = call i8* @strcat(i8* nonnull [[BUF]], i8* nonnull dereferenceable(1) [[SRC:%.*]])
+; NEWPM-NEXT:    call void @llvm.lifetime.end.p0i8(i64 256, i8* nonnull [[BUF]])
+; NEWPM-NEXT:    ret void
+;
+  %a = alloca [256 x i8], align 16
+  %buf = getelementptr inbounds [256 x i8], [256 x i8]* %a, i64 0, i64 0
+  call void @llvm.lifetime.start.p0i8(i64 256, i8* nonnull %buf)
+  call i8* @strcat(i8* nonnull %buf, i8* nonnull dereferenceable(1) %src)
+  call void @llvm.lifetime.end.p0i8(i64 256, i8* nonnull %buf)
+  ret void
+}
+
+define void @dse_strncat(i8* nocapture readonly %src) {
+; OLDPM-LABEL: @dse_strncat(
+; OLDPM-NEXT:    ret void
+;
+; NEWPM-LABEL: @dse_strncat(
+; NEWPM-NEXT:    [[A:%.*]] = alloca [256 x i8], align 16
+; NEWPM-NEXT:    [[BUF:%.*]] = getelementptr inbounds [256 x i8], [256 x i8]* [[A]], i64 0, i64 0
+; NEWPM-NEXT:    call void @llvm.lifetime.start.p0i8(i64 256, i8* nonnull [[BUF]])
+; NEWPM-NEXT:    [[TMP1:%.*]] = call i8* @strncat(i8* nonnull [[BUF]], i8* nonnull dereferenceable(1) [[SRC:%.*]], i64 6)
+; NEWPM-NEXT:    call void @llvm.lifetime.end.p0i8(i64 256, i8* nonnull [[BUF]])
+; NEWPM-NEXT:    ret void
+;
+  %a = alloca [256 x i8], align 16
+  %buf = getelementptr inbounds [256 x i8], [256 x i8]* %a, i64 0, i64 0
+  call void @llvm.lifetime.start.p0i8(i64 256, i8* nonnull %buf)
+  call i8* @strncat(i8* nonnull %buf, i8* nonnull dereferenceable(1) %src, i64 6)
+  call void @llvm.lifetime.end.p0i8(i64 256, i8* nonnull %buf)
+  ret void
+}
+
+declare void @llvm.lifetime.start.p0i8(i64 immarg, i8* nocapture)
+declare void @llvm.lifetime.end.p0i8(i64 immarg, i8* nocapture)
+