[PPC] Fix atomics lowering in DAG lowering.

I forgot to forward the chain, causing some missing instruction
dependencies. The test crashes the compiler without this patch.

Inspired by the test case, D33519 also tries to remove the extra sync.

Differential Revision: https://reviews.llvm.org/D33573

llvm-svn: 303931

1 files changed, 23 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/PowerPC/atomics-constant.ll b/llvm/test/CodeGen/PowerPC/atomics-constant.ll
new file mode 100644
index 00000000000..a92ca813af8
--- /dev/null
+++ b/llvm/test/CodeGen/PowerPC/atomics-constant.ll
@@ -0,0 +1,23 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s | FileCheck %s
+
+target triple = "powerpc64le-unknown-linux-gnu"
+
+@a = constant i64 zeroinitializer
+
+define i64 @foo() {
+; CHECK-LABEL: foo:
+; CHECK:       # BB#0: # %entry
+; CHECK-NEXT:    addis 3, 2, .LC0@toc@ha
+; CHECK-NEXT:    li 4, 0
+; CHECK-NEXT:    ld 3, .LC0@toc@l(3)
+; CHECK-NEXT:    cmpw 7, 4, 4
+; CHECK-NEXT:    ld 3, 0(3)
+; CHECK-NEXT:    bne- 7, .+4
+; CHECK-NEXT:    isync
+; CHECK-NEXT:    li 3, 0
+; CHECK-NEXT:    blr
+entry:
+  %value = load atomic i64, i64* @a acquire, align 8
+  ret i64 %value
+}