[StableHashing] Hash machine basic blocks and functions

[foad]

Summary

This adds very basic support for hashing MachineBasicBlock
and MachineFunction, for use in MachineFunctionPass to
detect passes that modify the MachineFunction wrongly.

[arsenm]

You're missing a lot of little fields that a pass could potentially change. e.g. block/function alignment, stack objects etc.

[foad]

In D120122#3335426, @arsenm wrote:

You're missing a lot of little fields that a pass could potentially change. e.g. block/function alignment, stack objects etc.

Yes. The same is true of the IR level structural hashing that is used for the same purpose (D86589). I was hoping to start with something simple like this, and it can always be improved in the future.

[arsenm]

In D120122#3335440, @foad wrote:

In D120122#3335426, @arsenm wrote:

You're missing a lot of little fields that a pass could potentially change. e.g. block/function alignment, stack objects etc.

Yes. The same is true of the IR level structural hashing that is used for the same purpose (D86589). I was hoping to start with something simple like this, and it can always be improved in the future.

Can you add a TODO for these sorts of things? I think it's too easy to not notice them here

[foad]

Add TODOs.

llvm/include/llvm/CodeGen/MachineStableHash.h

 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_CODEGEN_MACHINESTABLEHASH_H
 #define LLVM_CODEGEN_MACHINESTABLEHASH_H
 
 #include "llvm/CodeGen/StableHashing.h"
 
 namespace llvm {
+class MachineBasicBlock;
+class MachineFunction;
 class MachineInstr;
 class MachineOperand;
 
 stable_hash stableHashValue(const MachineOperand &MO);
 stable_hash stableHashValue(const MachineInstr &MI, bool HashVRegs = false,
                             bool HashConstantPoolIndices = false,
                             bool HashMemOperands = false);
+stable_hash stableHashValue(const MachineBasicBlock &MBB);
+stable_hash stableHashValue(const MachineFunction &MF);
 
 } // namespace llvm
 
 #endif

llvm/lib/CodeGen/MachineStableHash.cpp

for (const auto *Op : MI.memoperands()) {
     HashComponents.push_back(static_cast<unsigned>(Op->getSyncScopeID()));
     HashComponents.push_back(static_cast<unsigned>(Op->getBaseAlign().value()));
     HashComponents.push_back(static_cast<unsigned>(Op->getFailureOrdering()));
   }
 
   return stable_hash_combine_range(HashComponents.begin(),
                                    HashComponents.end());
 }
+
+stable_hash llvm::stableHashValue(const MachineBasicBlock &MBB) {
+  SmallVector<stable_hash> HashComponents;
+  // TODO: Hash more stuff like block alignment and branch probabilities.
+  for (auto &MI : MBB)
+    HashComponents.push_back(stableHashValue(MI));
+  return stable_hash_combine_range(HashComponents.begin(),
+                                   HashComponents.end());
+}
+
+stable_hash llvm::stableHashValue(const MachineFunction &MF) {
+  SmallVector<stable_hash> HashComponents;
+  // TODO: Hash lots more stuff like function alignment and stack objects.
+  for (auto &MBB : MF)
+    HashComponents.push_back(stableHashValue(MBB));
+  return stable_hash_combine_range(HashComponents.begin(),
+                                   HashComponents.end());
+}