Change the default latency for implicit defs.

Implicit defs are not currently positional and not modeled by the
per-operand machine model. Unfortunately, we treat defs that are part
of the architectural instruction description, like flags, the same as
other implicit defs. Really, they should have a fixed MachineInstr
layout and probably shouldn't be "implicit" at all.

For now, we'll change the default latency to be the max operand
latency. That will give flag setting operands full latency for x86
folded loads. Other kinds of "fake" implicit defs don't occur prior to
regalloc anyway, and we would like them to go away postRegAlloc as
well.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@177227 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 4 insertions, 1 deletions

diff --git a/lib/CodeGen/TargetSchedule.cpp b/lib/CodeGen/TargetSchedule.cpp
index f31f67d58c..783bfa1c1a 100644
--- a/lib/CodeGen/TargetSchedule.cpp
+++ b/lib/CodeGen/TargetSchedule.cpp
@@ -240,7 +240,10 @@ unsigned TargetSchedModel::computeOperandLatency(
     report_fatal_error(ss.str());
   }
 #endif
-  return DefMI->isTransient() ? 0 : 1;
+  // FIXME: Automatically giving all implicit defs defaultDefLatency is
+  // undesirable. We should only do it for defs that are known to the MC
+  // desc like flags. Truly implicit defs should get 1 cycle latency.
+  return DefMI->isTransient() ? 0 : TII->defaultDefLatency(&SchedModel, DefMI);
 }
 
 unsigned TargetSchedModel::computeInstrLatency(const MachineInstr *MI) const {