Improve on r192635, ExeDepsFix for avx, and add a test case.

rdar:15221834 False AVX register dependencies cause 5x slowdown on
flops-5/6 and significant slowdown on several others.

This was blocking the switch to MI-Sched.

llvm-svn: 192669

1 files changed, 3 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/ExecutionDepsFix.cpp b/llvm/lib/CodeGen/ExecutionDepsFix.cpp
index 0d26f9d4cba..031f19c135a 100644
--- a/llvm/lib/CodeGen/ExecutionDepsFix.cpp
+++ b/llvm/lib/CodeGen/ExecutionDepsFix.cpp
@@ -557,6 +557,9 @@ void ExeDepsFix::processUndefReads(MachineBasicBlock *MBB) {
 
   for (MachineBasicBlock::reverse_iterator I = MBB->rbegin(), E = MBB->rend();
        I != E; ++I) {
+    // Update liveness, including the current instrucion's defs.
+    LiveUnits.stepBackward(*I, *TRI);
+
     if (UndefMI == &*I) {
       if (!LiveUnits.contains(UndefMI->getOperand(OpIdx).getReg(), *TRI))
         TII->breakPartialRegDependency(UndefMI, OpIdx, TRI);
@@ -568,7 +571,6 @@ void ExeDepsFix::processUndefReads(MachineBasicBlock *MBB) {
       UndefMI = UndefReads.back().first;
       OpIdx = UndefReads.back().second;
     }
-    LiveUnits.stepBackward(*I, *TRI);
   }
 }