[llvm] [MCA] Parameterize variant scheduling classes by explicit variable (PR #92849)

[Aiden Grossman via llvm-commits]

================
@@ -185,3 +188,49 @@ TEST_F(X86TestBase, TestInstructionRecycling) {
     ASSERT_EQ(*BV, *V) << "Value of '" << F << "' does not match";
   }
 }
+
+// Test that we do not depend upon the MCInst address for variant description
+// construction. This test creates two instructions that will use variant
+// description as they are both zeroing idioms, but write to different
+// registers. If the key used to access the variant instruction description is
+// the same between the descriptions (like the MCInst pointer), we will run into
+// an assertion failure due to the different writes.
----------------
boomanaiden154 wrote:

Were you building with assertions enabled? The test would pass if assertions are not enabled. I hit an assertion with the following diff:
```patch
diff --git a/llvm/include/llvm/MCA/InstrBuilder.h b/llvm/include/llvm/MCA/InstrBuilder.h
index 9bfb8c0d2fca..e514b2afe584 100644
--- a/llvm/include/llvm/MCA/InstrBuilder.h
+++ b/llvm/include/llvm/MCA/InstrBuilder.h
@@ -74,7 +74,7 @@ class InstrBuilder {
 
   // Key is a hash of the MCInstruction and a SchedClassID that describe the
   // value InstrDesc
-  DenseMap<std::pair<hash_code, unsigned>, std::unique_ptr<const InstrDesc>>
+  DenseMap<std::pair<uint64_t, unsigned>, std::unique_ptr<const InstrDesc>>
       VariantDescriptors;
 
   bool FirstCallInst;
diff --git a/llvm/lib/MCA/InstrBuilder.cpp b/llvm/lib/MCA/InstrBuilder.cpp
index 8222d4a2d8e5..0194aeece4f7 100644
--- a/llvm/lib/MCA/InstrBuilder.cpp
+++ b/llvm/lib/MCA/InstrBuilder.cpp
@@ -624,7 +624,7 @@ InstrBuilder::createInstrDescImpl(const MCInst &MCI,
     return *Descriptors[DKey];
   }
 
-  auto VDKey = std::make_pair(hashMCInst(MCI), SchedClassID);
+  auto VDKey = std::make_pair(reinterpret_cast<uint64_t>(&MCI), SchedClassID);
   VariantDescriptors[VDKey] = std::move(ID);
   return *VariantDescriptors[VDKey];
 }
@@ -641,7 +641,7 @@ InstrBuilder::getOrCreateInstrDesc(const MCInst &MCI,
 
   unsigned CPUID = STI.getSchedModel().getProcessorID();
   SchedClassID = STI.resolveVariantSchedClass(SchedClassID, &MCI, &MCII, CPUID);
-  auto VDKey = std::make_pair(hashMCInst(MCI), SchedClassID);
+  auto VDKey = std::make_pair(reinterpret_cast<uint64_t>(&MCI), SchedClassID);
   if (VariantDescriptors.contains(VDKey))
     return *VariantDescriptors[VDKey];
```

https://github.com/llvm/llvm-project/pull/92849