From ace7ae935ffc181b79d5a22d58589949191b3416 Mon Sep 17 00:00:00 2001
From: Martin Storsjo <martin@martin.st>
Date: Mon, 14 May 2018 21:32:52 +0000
Subject: [PATCH] [ARM] Back up R4 and LR if calling the stack probe function

Differential Revision: https://reviews.llvm.org/D46777

llvm-svn: 332298
---
 llvm/lib/Target/ARM/ARMFrameLowering.cpp              | 11 +++++++++++
 .../test/CodeGen/ARM/Windows/chkstk-movw-movt-isel.ll |  2 +-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Target/ARM/ARMFrameLowering.cpp b/llvm/lib/Target/ARM/ARMFrameLowering.cpp
index 1b2c845c7b55..f350f3e8b30e 100644
--- a/llvm/lib/Target/ARM/ARMFrameLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMFrameLowering.cpp
@@ -1620,6 +1620,17 @@ void ARMFrameLowering::determineCalleeSaves(MachineFunction &MF,
       (MFI.hasVarSizedObjects() || RegInfo->needsStackRealignment(MF)))
     SavedRegs.set(ARM::R4);
 
+  // If a stack probe will be emitted, spill R4 and LR, since they are
+  // clobbered by the stack probe call.
+  // This estimate should be a safe, conservative estimate. The actual
+  // stack probe is enabled based on the size of the local objects;
+  // this estimate also includes the varargs store size.
+  if (STI.isTargetWindows() &&
+      WindowsRequiresStackProbe(MF, MFI.estimateStackSize(MF))) {
+    SavedRegs.set(ARM::R4);
+    SavedRegs.set(ARM::LR);
+  }
+
   if (AFI->isThumb1OnlyFunction()) {
     // Spill LR if Thumb1 function uses variable length argument lists.
     if (AFI->getArgRegsSaveSize() > 0)
diff --git a/llvm/test/CodeGen/ARM/Windows/chkstk-movw-movt-isel.ll b/llvm/test/CodeGen/ARM/Windows/chkstk-movw-movt-isel.ll
index a73a7cf8414f..019298d20808 100644
--- a/llvm/test/CodeGen/ARM/Windows/chkstk-movw-movt-isel.ll
+++ b/llvm/test/CodeGen/ARM/Windows/chkstk-movw-movt-isel.ll
@@ -18,7 +18,7 @@ entry:
 }
 
 ; CHECK-LABEL: isel
-; CHECK: push {r4, r5}
+; CHECK: push {r4, r5, r6, lr}
 ; CHECK: movw r12, #0
 ; CHECK: movt r12, #0
 ; CHECK: movw r4, #{{\d*}}