From 2615b686d3ecfa2354edb60ead0c72c5a2e88dd4 Mon Sep 17 00:00:00 2001
From: Ahmed Bougacha <ahmed.bougacha@gmail.com>
Date: Fri, 27 Mar 2015 20:28:30 +0000
Subject: [PATCH] [CodeGen] Don't attempt a tail-call with implicit sret.

Tailcalls are only OK with forwarded sret pointers. With sret demotion,
they're not, as we'd have a pointer into a soon-to-be-dead stack frame.

Differential Revison: http://reviews.llvm.org/D8510


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233409 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../SelectionDAG/SelectionDAGBuilder.cpp      |  4 ++
 .../CodeGen/AArch64/tailcall-implicit-sret.ll | 46 +++++++++++++++++++
 2 files changed, 50 insertions(+)
 create mode 100644 test/CodeGen/AArch64/tailcall-implicit-sret.ll

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 6a08fff09cd..67ab5482359 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -7193,6 +7193,10 @@ TargetLowering::LowerCallTo(TargetLowering::CallLoweringInfo &CLI) const {
     Entry.Alignment = Align;
     CLI.getArgs().insert(CLI.getArgs().begin(), Entry);
     CLI.RetTy = Type::getVoidTy(CLI.RetTy->getContext());
+
+    // sret demotion isn't compatible with tail-calls, since the sret argument
+    // points into the callers stack frame.
+    CLI.IsTailCall = false;
   } else {
     for (unsigned I = 0, E = RetTys.size(); I != E; ++I) {
       EVT VT = RetTys[I];
diff --git a/test/CodeGen/AArch64/tailcall-implicit-sret.ll b/test/CodeGen/AArch64/tailcall-implicit-sret.ll
new file mode 100644
index 00000000000..5d6805998d2
--- /dev/null
+++ b/test/CodeGen/AArch64/tailcall-implicit-sret.ll
@@ -0,0 +1,46 @@
+; RUN: llc < %s -mtriple arm64-apple-darwin -aarch64-load-store-opt=false -asm-verbose=false | FileCheck %s
+; Disable the load/store optimizer to avoid having LDP/STPs and simplify checks.
+
+target datalayout = "e-m:o-i64:64-i128:128-n32:64-S128"
+
+; Check that we don't try to tail-call with an sret-demoted return.
+
+declare i1024 @test_sret() #0
+
+; CHECK-LABEL: _test_call_sret:
+; CHECK: mov  x[[CALLERX8NUM:[0-9]+]], x8
+; CHECK: mov  x8, sp
+; CHECK-NEXT: bl _test_sret
+; CHECK-NEXT: ldr [[CALLERSRET1:x[0-9]+]], [sp]
+; CHECK: str [[CALLERSRET1:x[0-9]+]], [x[[CALLERX8NUM]]]
+; CHECK: ret
+define i1024 @test_call_sret() #0 {
+  %a = call i1024 @test_sret()
+  ret i1024 %a
+}
+
+; CHECK-LABEL: _test_tailcall_sret:
+; CHECK: mov  x[[CALLERX8NUM:[0-9]+]], x8
+; CHECK: mov  x8, sp
+; CHECK-NEXT: bl _test_sret
+; CHECK-NEXT: ldr [[CALLERSRET1:x[0-9]+]], [sp]
+; CHECK: str [[CALLERSRET1:x[0-9]+]], [x[[CALLERX8NUM]]]
+; CHECK: ret
+define i1024 @test_tailcall_sret() #0 {
+  %a = tail call i1024 @test_sret()
+  ret i1024 %a
+}
+
+; CHECK-LABEL: _test_indirect_tailcall_sret:
+; CHECK: mov  x[[CALLERX8NUM:[0-9]+]], x8
+; CHECK: mov  x8, sp
+; CHECK-NEXT: blr x0
+; CHECK-NEXT: ldr [[CALLERSRET1:x[0-9]+]], [sp]
+; CHECK: str [[CALLERSRET1:x[0-9]+]], [x[[CALLERX8NUM]]]
+; CHECK: ret
+define i1024 @test_indirect_tailcall_sret(i1024 ()* %f) #0 {
+  %a = tail call i1024 %f()
+  ret i1024 %a
+}
+
+attributes #0 = { nounwind }
-- 
2.34.1