[Attributor] Use nofree argument attribute for heap-to-stack conversion

Reviewers: jdoerfert, uenoku

Subscribers:

Differential Revision: https://reviews.llvm.org/D70140

2 files changed, 25 insertions, 11 deletions

diff --git a/llvm/lib/Transforms/IPO/Attributor.cpp b/llvm/lib/Transforms/IPO/Attributor.cpp
index db6a07ba46d..0e1f2e97d8f 100644
--- a/llvm/lib/Transforms/IPO/Attributor.cpp
+++ b/llvm/lib/Transforms/IPO/Attributor.cpp
@@ -4155,11 +4155,6 @@ ChangeStatus AAHeapToStackImpl::updateImpl(Attributor &A) {
         continue;
       }
 
-      // NOTE: Right now, if a function that has malloc pointer as an argument
-      // frees memory, we assume that the malloc pointer is freed.
-
-      // TODO: Add nofree callsite argument attribute to indicate that pointer
-      // argument is not freed.
       if (auto *CB = dyn_cast<CallBase>(UserI)) {
         if (!CB->isArgOperand(U))
           continue;
@@ -4180,15 +4175,16 @@ ChangeStatus AAHeapToStackImpl::updateImpl(Attributor &A) {
           continue;
         }
 
-        // If a function does not free memory we are fine
-        const auto &NoFreeAA =
-            A.getAAFor<AANoFree>(*this, IRPosition::callsite_function(*CB));
-
         unsigned ArgNo = CB->getArgOperandNo(U);
+
         const auto &NoCaptureAA = A.getAAFor<AANoCapture>(
             *this, IRPosition::callsite_argument(*CB, ArgNo));
 
-        if (!NoCaptureAA.isAssumedNoCapture() || !NoFreeAA.isAssumedNoFree()) {
+        // If a callsite argument use is nofree, we are fine.
+        const auto &ArgNoFreeAA = A.getAAFor<AANoFree>(
+            *this, IRPosition::callsite_argument(*CB, ArgNo));
+
+        if (!NoCaptureAA.isAssumedNoCapture() || !ArgNoFreeAA.isAssumedNoFree()) {
           LLVM_DEBUG(dbgs() << "[H2S] Bad user: " << *UserI << "\n");
           ValidUsesOnly = false;
         }
diff --git a/llvm/test/Transforms/FunctionAttrs/heap_to_stack.ll b/llvm/test/Transforms/FunctionAttrs/heap_to_stack.ll
index 83d072e912f..1f7be75ef16 100644
--- a/llvm/test/Transforms/FunctionAttrs/heap_to_stack.ll
+++ b/llvm/test/Transforms/FunctionAttrs/heap_to_stack.ll
@@ -24,6 +24,13 @@ declare void @free(i8* nocapture)
 
 declare void @llvm.lifetime.start.p0i8(i64, i8* nocapture) nounwind
 
+; CHECK: @nofree_arg_only(i8* nocapture nofree %p1, i8* nocapture %p2)
+define void @nofree_arg_only(i8* %p1, i8* %p2) {
+  tail call void @free(i8* %p2)
+  tail call void @nofree_func(i8* %p1)
+  ret void
+}
+
 ; TEST 1 - negative, pointer freed in another function.
 
 define void @test1() {
@@ -59,6 +66,16 @@ define void @test3() {
   ret void
 }
 
+define void @test3a(i8* %p) {
+  %1 = tail call noalias i8* @malloc(i64 4)
+  ; CHECK: %1 = alloca i8, i64 4
+  ; CHECK-NEXT: tail call void @nofree_arg_only
+  tail call void @nofree_arg_only(i8* %1, i8* %p)
+  ; CHECK-NOT: @free(i8* %1)
+  tail call void @free(i8* %1)
+  ret void
+}
+
 declare noalias i8* @calloc(i64, i64)
 
 define void @test0() {
@@ -85,7 +102,7 @@ define void @test4() {
 ; TEST 5 - not all exit paths have a call to free, but all uses of malloc
 ; are in nofree functions and are not captured
 
-define void @test5(i32) {
+define void @test5(i32, i8* %p) {
   %2 = tail call noalias i8* @malloc(i64 4)
   ; CHECK: %2 = alloca i8, i64 4
   ; CHECK-NEXT: icmp eq i32 %0, 0
@@ -97,6 +114,7 @@ define void @test5(i32) {
   br label %6
 
 5:                                                ; preds = %1
+  tail call void @nofree_arg_only(i8* %2, i8* %p)
   tail call void @free(i8* %2)
   ; CHECK-NOT: @free(i8* %2)
   br label %6