ARM SelectDYN_ALLOC should emit a copy from SP rather than referencing SP directly. In cases where there are two dyn_alloc in the same BB it would have caused the old SP value to be reused and badness ensues. rdar://7493908

llvm is generating poor code for dynamic alloca, I'll fix that later.

llvm-svn: 101383

2 files changed, 24 insertions, 1 deletions

diff --git a/llvm/lib/Target/ARM/ARMISelDAGToDAG.cpp b/llvm/lib/Target/ARM/ARMISelDAGToDAG.cpp
index 7d486631897..2f24d2ea1c6 100644
--- a/llvm/lib/Target/ARM/ARMISelDAGToDAG.cpp
+++ b/llvm/lib/Target/ARM/ARMISelDAGToDAG.cpp
@@ -945,7 +945,7 @@ SDNode *ARMDAGToDAGISel::SelectDYN_ALLOC(SDNode *N) {
   SDValue Chain = N->getOperand(0);
   SDValue Size = N->getOperand(1);
   SDValue Align = N->getOperand(2);
-  SDValue SP = CurDAG->getRegister(ARM::SP, MVT::i32);
+  SDValue SP = CurDAG->getCopyFromReg(Chain, dl, ARM::SP, MVT::i32);
   int32_t AlignVal = cast<ConstantSDNode>(Align)->getSExtValue();
   if (AlignVal < 0)
     // We need to align the stack. Use Thumb1 tAND which is the only thumb
diff --git a/llvm/test/CodeGen/Thumb2/2010-04-15-DynAllocBug.ll b/llvm/test/CodeGen/Thumb2/2010-04-15-DynAllocBug.ll
new file mode 100644
index 00000000000..329494b3219
--- /dev/null
+++ b/llvm/test/CodeGen/Thumb2/2010-04-15-DynAllocBug.ll
@@ -0,0 +1,23 @@
+; RUN: llc < %s -mtriple=thumbv7-apple-darwin -mcpu=cortex-a8 -O3 | FileCheck %s
+; rdar://7493908
+
+; Make sure the result of the first dynamic_alloc isn't copied back to sp more
+; than once. We'll deal with poor codegen later.
+
+define arm_apcscc void @t() nounwind ssp {
+entry:
+; CHECK: t:
+; CHECK: mvn r0, #7
+; CHECK: ands sp, r0
+; CHECK: mov r1, sp
+; CHECK: mov sp, r1
+; Yes, this is stupid codegen, but it's correct.
+; CHECK: sub sp, #16
+; CHECK: mov r1, sp
+; CHECK: mov sp, r1
+; CHECK: ands sp, r0
+  %size = mul i32 8, 2
+  %vla_a = alloca i8, i32 %size, align 8
+  %vla_b = alloca i8, i32 %size, align 8
+  unreachable
+}