Don't build up std::vectors with constant sizes when an array suffices.

NFC.

llvm-svn: 298701
diff --git a/llvm/lib/Target/AMDGPU/SIMachineScheduler.cpp b/llvm/lib/Target/AMDGPU/SIMachineScheduler.cpp
index da86bbf..bd3e46d 100644
--- a/llvm/lib/Target/AMDGPU/SIMachineScheduler.cpp
+++ b/llvm/lib/Target/AMDGPU/SIMachineScheduler.cpp
@@ -1825,7 +1825,9 @@
   // if VGPR usage is extremely high, try other good performing variants
   // which could lead to lower VGPR usage
   if (Best.MaxVGPRUsage > 180) {
-    std::vector<std::pair<SISchedulerBlockCreatorVariant, SISchedulerBlockSchedulerVariant>> Variants = {
+    static constexpr std::pair<SISchedulerBlockCreatorVariant,
+                               SISchedulerBlockSchedulerVariant>
+        Variants[] = {
       { LatenciesAlone, BlockRegUsageLatency },
 //      { LatenciesAlone, BlockRegUsage },
       { LatenciesGrouped, BlockLatencyRegUsage },
@@ -1844,7 +1846,9 @@
   // if VGPR usage is still extremely high, we may spill. Try other variants
   // which are less performing, but that could lead to lower VGPR usage.
   if (Best.MaxVGPRUsage > 200) {
-    std::vector<std::pair<SISchedulerBlockCreatorVariant, SISchedulerBlockSchedulerVariant>> Variants = {
+    static constexpr std::pair<SISchedulerBlockCreatorVariant,
+                               SISchedulerBlockSchedulerVariant>
+        Variants[] = {
 //      { LatenciesAlone, BlockRegUsageLatency },
       { LatenciesAlone, BlockRegUsage },
 //      { LatenciesGrouped, BlockLatencyRegUsage },