Index: llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2560,6 +2560,42 @@
   return isAllocLikeFn(V, TLI) && V != AI;
 }
 
+/// Given a call CB which uses an address UsedV, return true if we can prove the
+/// calls only effect is storing to V.
+static bool isRemovableWrite(CallBase &CB, Value *UsedV) {
+  if (!CB.use_empty())
+    // TODO: add recursion if returned attribute is present
+    return false;
+
+  if (!CB.willReturn() || !CB.doesNotThrow() || !CB.onlyAccessesArgMemory() ||
+      CB.isTerminator())
+    return false;
+
+  if (CB.hasOperandBundles())
+    return false;
+
+  for (unsigned i = 0; i < CB.arg_size(); i++) {
+    if (!CB.getArgOperand(i)->getType()->isPointerTy())
+      continue;
+    if (!CB.doesNotCapture(i))
+      // capture would allow the address to be read back in an untracked manner
+      return false;
+    if (UsedV != CB.getArgOperand(i)) {
+      if (!CB.onlyReadsMemory(i))
+        // A write to another memory location keeps the call live, and thus we
+        // must keep the alloca so that the call has somewhere to write to.
+        // TODO: This results in an inprecision when two values derived from the
+        // same alloca are passed as arguments to the same function.
+        return false;
+      continue;
+    }
+    if (!CB.paramHasAttr(i, Attribute::WriteOnly))
+      // a read would hold the address live
+      return false;
+  }
+  return true;
+}
+
 static bool isAllocSiteRemovable(Instruction *AI,
                                  SmallVectorImpl<WeakTrackingVH> &Users,
                                  const TargetLibraryInfo *TLI) {
@@ -2627,6 +2663,11 @@
           }
         }
 
+        if (isRemovableWrite(*cast<CallBase>(I), PI)) {
+          Users.emplace_back(I);
+          continue;
+        }
+
         if (isFreeCall(I, TLI)) {
           Users.emplace_back(I);
           continue;
Index: llvm/test/Transforms/InstCombine/trivial-dse-calls.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/InstCombine/trivial-dse-calls.ll
@@ -0,0 +1,200 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -instcombine -S < %s | FileCheck %s
+
+declare void @llvm.lifetime.start.p0i8(i64 immarg, i8* nocapture)
+declare void @llvm.lifetime.end.p0i8(i64 immarg, i8* nocapture)
+
+declare void @unknown()
+declare void @f(i8*)
+declare void @f2(i8*, i8*)
+
+; Basic case for DSEing a trivially dead writing call
+define void @test_dead() {
+; CHECK-LABEL: @test_dead(
+; CHECK-NEXT:    ret void
+;
+  %a = alloca i32, align 4
+  %bitcast = bitcast i32* %a to i8*
+  call void @f(i8* writeonly nocapture %bitcast) argmemonly nounwind willreturn
+  ret void
+}
+
+; Add in canonical lifetime intrinsics
+define void @test_lifetime() {
+; CHECK-LABEL: @test_lifetime(
+; CHECK-NEXT:    ret void
+;
+  %a = alloca i32, align 4
+  %bitcast = bitcast i32* %a to i8*
+  call void @llvm.lifetime.start.p0i8(i64 4, i8* %bitcast)
+  call void @f(i8* writeonly nocapture %bitcast) argmemonly nounwind willreturn
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* %bitcast)
+  ret void
+}
+
+; Add some unknown calls just to point out that this is use based, not
+; instruction order sensitive
+define void @test_lifetime2() {
+; CHECK-LABEL: @test_lifetime2(
+; CHECK-NEXT:    call void @unknown()
+; CHECK-NEXT:    call void @unknown()
+; CHECK-NEXT:    ret void
+;
+  %a = alloca i32, align 4
+  %bitcast = bitcast i32* %a to i8*
+  call void @llvm.lifetime.start.p0i8(i64 4, i8* %bitcast)
+  call void @unknown()
+  call void @f(i8* writeonly nocapture %bitcast) argmemonly nounwind willreturn
+  call void @unknown()
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* %bitcast)
+  ret void
+}
+
+define i32 @test_neg_read_after() {
+; CHECK-LABEL: @test_neg_read_after(
+; CHECK-NEXT:    [[A:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    [[BITCAST:%.*]] = bitcast i32* [[A]] to i8*
+; CHECK-NEXT:    call void @f(i8* nocapture nonnull writeonly [[BITCAST]]) #[[ATTR1:[0-9]+]]
+; CHECK-NEXT:    [[RES:%.*]] = load i32, i32* [[A]], align 4
+; CHECK-NEXT:    ret i32 [[RES]]
+;
+  %a = alloca i32, align 4
+  %bitcast = bitcast i32* %a to i8*
+  call void @f(i8* writeonly nocapture %bitcast) argmemonly nounwind willreturn
+  %res = load i32, i32* %a
+  ret i32 %res
+}
+
+
+define void @test_neg_infinite_loop() {
+; CHECK-LABEL: @test_neg_infinite_loop(
+; CHECK-NEXT:    [[A:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    [[BITCAST:%.*]] = bitcast i32* [[A]] to i8*
+; CHECK-NEXT:    call void @f(i8* nocapture nonnull writeonly [[BITCAST]]) #[[ATTR2:[0-9]+]]
+; CHECK-NEXT:    ret void
+;
+  %a = alloca i32, align 4
+  %bitcast = bitcast i32* %a to i8*
+  call void @f(i8* writeonly nocapture %bitcast) argmemonly nounwind
+  ret void
+}
+
+define void @test_neg_throw() {
+; CHECK-LABEL: @test_neg_throw(
+; CHECK-NEXT:    [[A:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    [[BITCAST:%.*]] = bitcast i32* [[A]] to i8*
+; CHECK-NEXT:    call void @f(i8* nocapture nonnull writeonly [[BITCAST]]) #[[ATTR3:[0-9]+]]
+; CHECK-NEXT:    ret void
+;
+  %a = alloca i32, align 4
+  %bitcast = bitcast i32* %a to i8*
+  call void @f(i8* writeonly nocapture %bitcast) argmemonly willreturn
+  ret void
+}
+
+define void @test_neg_extra_write() {
+; CHECK-LABEL: @test_neg_extra_write(
+; CHECK-NEXT:    [[A:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    [[BITCAST:%.*]] = bitcast i32* [[A]] to i8*
+; CHECK-NEXT:    call void @f(i8* nocapture nonnull writeonly [[BITCAST]]) #[[ATTR4:[0-9]+]]
+; CHECK-NEXT:    ret void
+;
+  %a = alloca i32, align 4
+  %bitcast = bitcast i32* %a to i8*
+  call void @f(i8* writeonly nocapture %bitcast) nounwind willreturn
+  ret void
+}
+
+; In this case, we can't remove a1 because we need to preserve the write to
+; a2, and if we leave the call around, we need memory to pass to the first arg.
+define void @test_neg_unmodeled_write() {
+; CHECK-LABEL: @test_neg_unmodeled_write(
+; CHECK-NEXT:    [[A:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    [[A2:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    [[BITCAST:%.*]] = bitcast i32* [[A]] to i8*
+; CHECK-NEXT:    [[BITCAST2:%.*]] = bitcast i32* [[A2]] to i8*
+; CHECK-NEXT:    call void @f2(i8* nocapture nonnull writeonly [[BITCAST]], i8* nonnull [[BITCAST2]]) #[[ATTR1]]
+; CHECK-NEXT:    ret void
+;
+  %a = alloca i32, align 4
+  %a2 = alloca i32, align 4
+  %bitcast = bitcast i32* %a to i8*
+  %bitcast2 = bitcast i32* %a2 to i8*
+  call void @f2(i8* nocapture writeonly %bitcast, i8* %bitcast2) argmemonly nounwind willreturn
+  ret void
+}
+
+define i32 @test_neg_captured_by_call() {
+; CHECK-LABEL: @test_neg_captured_by_call(
+; CHECK-NEXT:    [[A:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    [[A2:%.*]] = alloca i8*, align 8
+; CHECK-NEXT:    [[BITCAST:%.*]] = bitcast i32* [[A]] to i8*
+; CHECK-NEXT:    [[BITCAST2:%.*]] = bitcast i8** [[A2]] to i8*
+; CHECK-NEXT:    call void @f2(i8* nonnull writeonly [[BITCAST]], i8* nonnull [[BITCAST2]]) #[[ATTR1]]
+; CHECK-NEXT:    [[TMP1:%.*]] = bitcast i8** [[A2]] to i32**
+; CHECK-NEXT:    [[A_COPY_CAST1:%.*]] = load i32*, i32** [[TMP1]], align 8
+; CHECK-NEXT:    [[RES:%.*]] = load i32, i32* [[A_COPY_CAST1]], align 4
+; CHECK-NEXT:    ret i32 [[RES]]
+;
+  %a = alloca i32, align 4
+  %a2 = alloca i8*, align 4
+  %bitcast = bitcast i32* %a to i8*
+  %bitcast2 = bitcast i8** %a2 to i8*
+  call void @f2(i8* writeonly %bitcast, i8* %bitcast2) argmemonly nounwind willreturn
+  %a_copy_cast = load i8*, i8** %a2
+  %a_copy = bitcast i8* %a_copy_cast to i32*
+  %res = load i32, i32* %a_copy
+  ret i32 %res
+}
+
+define i32 @test_neg_captured_before() {
+; CHECK-LABEL: @test_neg_captured_before(
+; CHECK-NEXT:    [[A:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    [[BITCAST:%.*]] = bitcast i32* [[A]] to i8*
+; CHECK-NEXT:    call void @f(i8* nocapture nonnull writeonly [[BITCAST]]) #[[ATTR1]]
+; CHECK-NEXT:    [[RES:%.*]] = load i32, i32* [[A]], align 4
+; CHECK-NEXT:    ret i32 [[RES]]
+;
+  %a = alloca i32, align 4
+  %a2 = alloca i8*, align 4
+  %bitcast = bitcast i32* %a to i8*
+  %bitcast2 = bitcast i8** %a2 to i8*
+  store i8* %bitcast, i8** %a2
+  call void @f(i8* writeonly nocapture %bitcast) argmemonly nounwind willreturn
+  %a_copy_cast = load i8*, i8** %a2
+  %a_copy = bitcast i8* %a_copy_cast to i32*
+  %res = load i32, i32* %a_copy
+  ret i32 %res
+}
+
+; Show that reading from unrelated memory is okay
+define void @test_unreleated_read() {
+; CHECK-LABEL: @test_unreleated_read(
+; CHECK-NEXT:    ret void
+;
+  %a = alloca i32, align 4
+  %a2 = alloca i32, align 4
+  %bitcast = bitcast i32* %a to i8*
+  %bitcast2 = bitcast i32* %a2 to i8*
+  call void @f2(i8* nocapture writeonly %bitcast, i8* nocapture readonly %bitcast2) argmemonly nounwind willreturn
+  ret void
+}
+
+; But that removing a capture of an unrelated pointer isn't okay.
+define void @test_neg_unreleated_capture() {
+; CHECK-LABEL: @test_neg_unreleated_capture(
+; CHECK-NEXT:    [[A:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    [[A2:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    [[BITCAST:%.*]] = bitcast i32* [[A]] to i8*
+; CHECK-NEXT:    [[BITCAST2:%.*]] = bitcast i32* [[A2]] to i8*
+; CHECK-NEXT:    call void @f2(i8* nocapture nonnull writeonly [[BITCAST]], i8* nonnull readonly [[BITCAST2]]) #[[ATTR1]]
+; CHECK-NEXT:    ret void
+;
+  %a = alloca i32, align 4
+  %a2 = alloca i32, align 4
+  %bitcast = bitcast i32* %a to i8*
+  %bitcast2 = bitcast i32* %a2 to i8*
+  call void @f2(i8* nocapture writeonly %bitcast, i8* readonly %bitcast2) argmemonly nounwind willreturn
+  ret void
+}
+