[llvm] [TableGen][GlobalISel] Add rule-wide type inference (PR #66377)

[Pierre van Houtryve via llvm-commits]

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@@ -1639,6 +1695,471 @@ class PrettyStackTraceEmit : public PrettyStackTraceEntry {
   }
 };
 
+//===- CombineRuleOperandTypeChecker --------------------------------------===//
+
+/// This is a wrapper around OperandTypeChecker specialized for Combiner Rules.
+/// On top of doing the same things as OperandTypeChecker, this also attempts to
+/// infer as many types as possible for temporary register defs & immediates in
+/// apply patterns.
+///
+/// The inference is trivial and leverages the MCOI OperandTypes encoded in
+/// CodeGenInstructions to infer types across patterns in a CombineRule. It's
+/// thus very limited and only supports CodeGenInstructions (but that's the main
+/// use case so it's fine).
+///
+/// We only try to infer untyped operands in apply patterns when they're temp
+/// reg defs, or immediates. Inference always outputs a `TypeOf<$x>` where $x is
+/// a named operand from a match pattern.
+class CombineRuleOperandTypeChecker : private OperandTypeChecker {
+public:
+  CombineRuleOperandTypeChecker(const Record &RuleDef,
+                                const OperandTable &MatchOpTable)
+      : OperandTypeChecker(RuleDef.getLoc()), RuleDef(RuleDef),
+        MatchOpTable(MatchOpTable) {}
+
+  /// Records and checks a 'match' pattern.
+  bool processMatchPattern(InstructionPattern &P);
+
+  /// Records and checks an 'apply' pattern.
+  bool processApplyPattern(InstructionPattern &P);
+
+  /// Propagates types, then perform type inference and do a second round of
+  /// propagation in the apply patterns only if any types were inferred.
+  void propagateAndInferTypes();
+
+private:
+  /// TypeEquivalenceClasses are groups of operands of an instruction that share
+  /// a common type.
+  ///
+  /// e.g. [[a, b], [c, d]] means a and b have the same type, and c and
+  /// d have the same type too. b/c and a/d don't have to have the same type,
+  /// though.
+  ///
+  /// NOTE: We use a SetVector, not a Set. This is to guarantee a stable
+  /// iteration order which is important because:
+  ///   - During inference, we iterate that set and pick the first suitable
+  ///   candidate. Using a normal set could make inference inconsistent across
+  ///   runs if the Set uses the StringRef ptr to cache values.
+  ///   - We print this set if DebugInfer is set, and we don't want our tests to
+  ///   fail randomly due to the Set's iteration order changing.
+  using TypeEquivalenceClasses = std::vector<SetVector<StringRef>>;
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Pierre-vh wrote:

I didn't know if it was a good fit at first so I just hand-wrote the logic, but indeed EquivalenceClasses is just perfect for this (and gets rid of the set operations)

https://github.com/llvm/llvm-project/pull/66377