[SystemZ] Bugfix of CC liveness in emitMemMemWrapper (CLC).

If DoneMBB becomes empty it must have CC added to its live-in list, since it
will fall-through into EndMBB. This happens when the CLC loop does the
complete range.

Review: Ulrich Weigand
llvm-svn: 327834

2 files changed, 24 insertions, 0 deletions

diff --git a/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp b/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
index bf2d1833515..5de324d1d46 100644
--- a/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
@@ -6626,6 +6626,10 @@ MachineBasicBlock *SystemZTargetLowering::emitMemMemWrapper(
     DestBase = MachineOperand::CreateReg(NextDestReg, false);
     SrcBase = MachineOperand::CreateReg(NextSrcReg, false);
     Length &= 255;
+    if (EndMBB && !Length)
+      // If the loop handled the whole CLC range, DoneMBB will be empty with
+      // CC live-through into EndMBB, so add it as live-in.
+      DoneMBB->addLiveIn(SystemZ::CC);
     MBB = DoneMBB;
   }
   // Handle any remaining bytes with straight-line code.
diff --git a/llvm/test/CodeGen/SystemZ/memcmp-02.ll b/llvm/test/CodeGen/SystemZ/memcmp-02.ll
new file mode 100644
index 00000000000..303e015ec99
--- /dev/null
+++ b/llvm/test/CodeGen/SystemZ/memcmp-02.ll
@@ -0,0 +1,20 @@
+; Test memcmp using CLC.  In this test case the CLC loop will do all the work
+; and the DoneMBB becomes empty. It will not pass the mischeduling verifiers
+; if DoneMBB does not have CC in its live-in list.
+
+; RUN: llc < %s -mtriple=s390x-linux-gnu -misched=shuffle | FileCheck %s
+
+declare i32 @memcmp(i8* nocapture, i8* nocapture, i64)
+
+define i32 @fun() {
+; CHECK-LABEL: fun
+  %call = call signext i32 @memcmp(i8* nonnull undef, i8* nonnull undef, i64 2048)
+  %cmp = icmp eq i32 %call, 0
+  br i1 %cmp, label %labT, label %labF
+
+labT:
+  ret i32 0
+
+labF:
+  ret i32 1
+}