AMDGPU: Avoid constructing new std::vector in initCandidate

Approximately 30% of the time was spent in the std::vector
constructor. In one testcase this pushes the scheduler to being the
second slowest pass.

I'm not sure I understand why these vector are necessary. The default
scheduler initCandidate seems to use some pre-existing vectors for the
pressure.

llvm-svn: 371136

1 files changed, 2 insertions, 2 deletions

diff --git a/llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp b/llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp
index 4ea990ae490..3861cc674e5 100644
--- a/llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp
+++ b/llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp
@@ -71,8 +71,8 @@ void GCNMaxOccupancySchedStrategy::initCandidate(SchedCandidate &Cand, SUnit *SU
   // the tracker, so we need to pass those function a non-const copy.
   RegPressureTracker &TempTracker = const_cast<RegPressureTracker&>(RPTracker);
 
-  std::vector<unsigned> Pressure;
-  std::vector<unsigned> MaxPressure;
+  Pressure.clear();
+  MaxPressure.clear();
 
   if (AtTop)
     TempTracker.getDownwardPressure(SU->getInstr(), Pressure, MaxPressure);