X86: VZeroUpperInserter: shortcut should not trigger if we have any function live-ins.

llvm-svn: 225419

1 files changed, 12 insertions, 8 deletions

diff --git a/llvm/lib/Target/X86/X86VZeroUpper.cpp b/llvm/lib/Target/X86/X86VZeroUpper.cpp
index d93baeb7002..5c01f3e1ff6 100644
--- a/llvm/lib/Target/X86/X86VZeroUpper.cpp
+++ b/llvm/lib/Target/X86/X86VZeroUpper.cpp
@@ -254,16 +254,20 @@ bool VZeroUpperInserter::runOnMachineFunction(MachineFunction &MF) {
   MachineRegisterInfo &MRI = MF.getRegInfo();
   EverMadeChange = false;
 
+  bool FnHasLiveInYmm = checkFnHasLiveInYmm(MRI);
+
   // Fast check: if the function doesn't use any ymm registers, we don't need
   // to insert any VZEROUPPER instructions.  This is constant-time, so it is
   // cheap in the common case of no ymm use.
-  bool YMMUsed = false;
-  const TargetRegisterClass *RC = &X86::VR256RegClass;
-  for (TargetRegisterClass::iterator i = RC->begin(), e = RC->end();
-       i != e; i++) {
-    if (!MRI.reg_nodbg_empty(*i)) {
-      YMMUsed = true;
-      break;
+  bool YMMUsed = FnHasLiveInYmm;
+  if (!YMMUsed) {
+    const TargetRegisterClass *RC = &X86::VR256RegClass;
+    for (TargetRegisterClass::iterator i = RC->begin(), e = RC->end(); i != e;
+         i++) {
+      if (!MRI.reg_nodbg_empty(*i)) {
+        YMMUsed = true;
+        break;
+      }
     }
   }
   if (!YMMUsed) {
@@ -282,7 +286,7 @@ bool VZeroUpperInserter::runOnMachineFunction(MachineFunction &MF) {
 
   // If any YMM regs are live in to this function, add the entry block to the
   // DirtySuccessors list
-  if (checkFnHasLiveInYmm(MRI))
+  if (FnHasLiveInYmm)
     addDirtySuccessor(MF.front());
 
   // Re-visit all blocks that are successors of EXITS_DIRTY bsocks. Add