[llvm] a8a7bf9 - [mlgo][regalloc] Fix register masking

[Mircea Trofin via llvm-commits]

Author: Mircea Trofin
Date: 2022-01-30T14:59:08-08:00
New Revision: a8a7bf922cea8af01168f7a4adf4ed0365bcc2b4

URL: https://github.com/llvm/llvm-project/commit/a8a7bf922cea8af01168f7a4adf4ed0365bcc2b4
DIFF: https://github.com/llvm/llvm-project/commit/a8a7bf922cea8af01168f7a4adf4ed0365bcc2b4.diff

LOG: [mlgo][regalloc] Fix register masking

If AllocationOrder has less than 32 elements, we were treating the extra
positions as if they were valid. This was detected by a subsequent
assert. The fix also tightens the asserts.

Added: 
    

Modified: 
    llvm/lib/CodeGen/MLRegallocEvictAdvisor.cpp

Removed: 
    


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diff  --git a/llvm/lib/CodeGen/MLRegallocEvictAdvisor.cpp b/llvm/lib/CodeGen/MLRegallocEvictAdvisor.cpp
index a74c57690640..f8ba224da7b8 100644
--- a/llvm/lib/CodeGen/MLRegallocEvictAdvisor.cpp
+++ b/llvm/lib/CodeGen/MLRegallocEvictAdvisor.cpp
@@ -615,16 +615,15 @@ MCRegister MLEvictAdvisor::tryFindEvictionCandidate(
   for (auto I = Order.begin(), E = Order.getOrderLimitEnd(OrderLimit); I != E;
        ++I, ++Pos) {
     MCRegister PhysReg = *I;
-    Regs[Pos] = std::make_pair(PhysReg, true);
+    assert(!Regs[Pos].second);
     assert(PhysReg);
     if (!canAllocatePhysReg(CostPerUseLimit, PhysReg)) {
-      Regs[Pos].second = false;
       continue;
     }
     if (loadInterferenceFeatures(VirtReg, PhysReg, I.isHint(), FixedRegisters,
                                  Largest, Pos)) {
       ++Available;
-      Regs[Pos].second = true;
+      Regs[Pos] = std::make_pair(PhysReg, true);
     }
   }
   if (Available == 0) {
@@ -632,6 +631,7 @@ MCRegister MLEvictAdvisor::tryFindEvictionCandidate(
     assert(!MustFindEviction);
     return MCRegister::NoRegister;
   }
+  const size_t ValidPosLimit = Pos;
   // If we must find eviction, the candidate should be masked out of the
   // decision making process.
   Regs[CandidateVirtRegPos].second = !MustFindEviction;
@@ -665,6 +665,7 @@ MCRegister MLEvictAdvisor::tryFindEvictionCandidate(
     assert(!MustFindEviction);
     return MCRegister::NoRegister;
   }
+  assert(CandidatePos < ValidPosLimit);
   return Regs[CandidatePos].first;
 }