From 3904343c68926f1ed8250e4a9b0863868f1ffb74 Mon Sep 17 00:00:00 2001
From: Eric Christopher <echristo@apple.com>
Date: Tue, 11 Jan 2011 00:16:04 +0000
Subject: [PATCH] Even if we don't have 7 bytes of stack space we may need to
 save and restore the stack pointer from the frame pointer on thumbv6.

Fixes rdar://8819685

llvm-svn: 123196
---
 llvm/lib/Target/ARM/Thumb1FrameLowering.cpp |  9 ++++-
 llvm/test/CodeGen/ARM/thumb1-varalloc.ll    | 40 +++++++++++++++++++++
 2 files changed, 48 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/CodeGen/ARM/thumb1-varalloc.ll

diff --git a/llvm/lib/Target/ARM/Thumb1FrameLowering.cpp b/llvm/lib/Target/ARM/Thumb1FrameLowering.cpp
index e3f2d2d5981f..8a6dda821484 100644
--- a/llvm/lib/Target/ARM/Thumb1FrameLowering.cpp
+++ b/llvm/lib/Target/ARM/Thumb1FrameLowering.cpp
@@ -156,6 +156,12 @@ void Thumb1FrameLowering::emitPrologue(MachineFunction &MF) const {
   // to reference locals.
   if (RegInfo->hasBasePointer(MF))
     BuildMI(MBB, MBBI, dl, TII.get(ARM::tMOVgpr2gpr), BasePtr).addReg(ARM::SP);
+    
+  // If the frame has variable sized objects then the epilogue must restore
+  // the sp from fp. We can assume there's an FP here since hasFP already
+  // checks for hasVarSizedObjects.
+  if (MFI->hasVarSizedObjects())
+    AFI->setShouldRestoreSPFromFP(true);
 }
 
 static bool isCalleeSavedRegister(unsigned Reg, const unsigned *CSRegs) {
@@ -221,7 +227,8 @@ void Thumb1FrameLowering::emitEpilogue(MachineFunction &MF,
     if (AFI->shouldRestoreSPFromFP()) {
       NumBytes = AFI->getFramePtrSpillOffset() - NumBytes;
       // Reset SP based on frame pointer only if the stack frame extends beyond
-      // frame pointer stack slot or target is ELF and the function has FP.
+      // frame pointer stack slot, the target is ELF and the function has FP, or
+      // the target uses var sized objects.
       if (NumBytes) {
         assert(MF.getRegInfo().isPhysRegUsed(ARM::R4) &&
                "No scratch register to restore SP from FP!");
diff --git a/llvm/test/CodeGen/ARM/thumb1-varalloc.ll b/llvm/test/CodeGen/ARM/thumb1-varalloc.ll
new file mode 100644
index 000000000000..25093fee225a
--- /dev/null
+++ b/llvm/test/CodeGen/ARM/thumb1-varalloc.ll
@@ -0,0 +1,40 @@
+; RUN: llc < %s -mtriple=thumbv6-apple-darwin | FileCheck %s
+; rdar://8819685
+
+@__bar = external hidden global i8*
+@__baz = external hidden global i8*
+
+define i8* @_foo() {
+entry:
+; CHECK: foo:
+
+	%size = alloca i32, align 4
+	%0 = load i8** @__bar, align 4
+	%1 = icmp eq i8* %0, null
+	br i1 %1, label %bb1, label %bb3
+		
+bb1:
+	store i32 1026, i32* %size, align 4
+	%2 = alloca [1026 x i8], align 1
+; CHECK: mov     r0, sp
+; CHECK: adds    r4, r0, r4
+	%3 = getelementptr inbounds [1026 x i8]* %2, i32 0, i32 0
+	%4 = call i32 @_called_func(i8* %3, i32* %size) nounwind
+	%5 = icmp eq i32 %4, 0
+	br i1 %5, label %bb2, label %bb3
+	
+bb2:
+	%6 = call i8* @strdup(i8* %3) nounwind
+	store i8* %6, i8** @__baz, align 4
+	br label %bb3
+	
+bb3:
+	%.0 = phi i8* [ %0, %entry ], [ %6, %bb2 ], [ %3, %bb1 ]
+; CHECK: subs    r4, #5
+; CHECK-NEXT: mov     sp, r4
+; CHECK-NEXT: pop     {r4, r5, r6, r7, pc}
+	ret i8* %.0
+}
+
+declare noalias i8* @strdup(i8* nocapture) nounwind
+declare i32 @_called_func(i8*, i32*) nounwind
\ No newline at end of file