[RegisterBankInfo] Remove overly-agressive asserts

Summary:
We were asserting in RegisterBankInfo if RBI.copyCost() returns
UINT_MAX.  This is OK for RegBankSelect::Mode::Fast since we only
try one instruction mapping and can't recover from this, but for
RegBankSelect::Mode::Greedy we will be considering multiple
instruction mappings, so we can recover if we see a UNIT_MAX copy
cost.

The copy cost for one pair of register banks in the AMDGPU backend
will be UNIT_MAX, so this patch will prevent AMDGPU tests from
breaking.

Reviewers: ab, qcolombet, t.p.northover, dsanders

Reviewed By: qcolombet

Subscribers: tpr, llvm-commits

Differential Revision: https://reviews.llvm.org/D33144

llvm-svn: 303043

llvm/lib/CodeGen/GlobalISel/RegBankSelect.cpp

@@ -204,12 +204,8 @@ uint64_t RegBankSelect::getRepairCost(
     // TODO: use a dedicated constant for ImpossibleCost.
     if (Cost != UINT_MAX)
       return Cost;
-    assert(!TPC->isGlobalISelAbortEnabled() &&
-           "Legalization not available yet");
     // Return the legalization cost of that repairing.
   }
-  assert(!TPC->isGlobalISelAbortEnabled() &&
-         "Complex repairing not implemented yet");
   return UINT_MAX;
 }
 
@@ -452,6 +448,11 @@ RegBankSelect::MappingCost RegBankSelect::computeMapping(
 
     // Sums up the repairing cost of MO at each insertion point.
     uint64_t RepairCost = getRepairCost(MO, ValMapping);
+
+    // This is an impossible to repair cost.
+    if (RepairCost == UINT_MAX)
+      continue;
+
     // Bias used for splitting: 5%.
     const uint64_t PercentageForBias = 5;
     uint64_t Bias = (RepairCost * PercentageForBias + 99) / 100;