[A57FPLoadBalancing] Modify r217689 - actually we do need to check defs

... Just make sure we check uses first so we see the kill first. It
turns out ignoring defs gives some pretty nasty runtime failures.
I'm certain this is the fix but I'm still reducing a testcase.

llvm-svn: 217735

Author: James Molloy

llvm/lib/Target/AArch64/AArch64A57FPLoadBalancing.cpp

@@ -582,7 +582,9 @@ scanInstruction(MachineInstr *MI, unsigned Idx,
 
   if (isMul(MI)) {
 
-    for (auto &I : MI->operands())
+    for (auto &I : MI->uses())
+      maybeKillChain(I, Idx, ActiveChains);
+    for (auto &I : MI->defs())
       maybeKillChain(I, Idx, ActiveChains);
 
     // Create a new chain. Multiplies don't require forwarding so can go on any
@@ -644,7 +646,9 @@ scanInstruction(MachineInstr *MI, unsigned Idx,
 
     // Non-MUL or MLA instruction. Invalidate any chain in the uses or defs
     // lists.
-    for (auto &I : MI->operands())
+    for (auto &I : MI->uses())
+      maybeKillChain(I, Idx, ActiveChains);
+    for (auto &I : MI->defs())
       maybeKillChain(I, Idx, ActiveChains);
 
   }
@@ -657,10 +661,6 @@ maybeKillChain(MachineOperand &MO, unsigned Idx,
   // determine if a chain should be ended and remove from ActiveChains.
   MachineInstr *MI = MO.getParent();
 
-  if (MO.isReg() && MO.isDef())
-    // We don't care about defs. We see them before uses, so reject them early.
-    return;
-
   if (MO.isReg()) {
 
     // If this is a KILL of a current chain, record it.