Rewrite IREquality to use a more compact stack instead of deep recurs…

…ion (#8198)

* Rewrite IREquality to use a more compact stack instead of deep recursion

Deletes a bunch of code and speeds up lowering time of local laplacian
with 20 pyramid levels by ~2.5%

* clang-tidy

* Fold in the version of equal in IRMatch.h/cpp

* Add missing switch breaks

* Add missing comments

* Elaborate on why we treat NaNs as equal

src/Associativity.cpp

@@ -145,7 +145,7 @@ bool associative_op_pattern_match(const Expr &e,
                 debug(5) << "Adding result: " << iter.first << " -> " << iter.second << "\n";
                 match.emplace(iter.first, iter.second);
             } else {
-                if (!equal(iter.first, match_iter->first) || !equal(iter.second, match_iter->second)) {
+                if (iter.first != match_iter->first || !equal(iter.second, match_iter->second)) {
                     return false;
                 }
             }

src/Bounds.cpp

@@ -79,9 +79,9 @@ int static_sign(const Expr &x) {
         return -1;
     } else {
         Expr zero = make_zero(x.type());
-        if (equal(const_true(), simplify(x > zero))) {
+        if (is_const_one(simplify(x > zero))) {
             return 1;
-        } else if (equal(const_true(), simplify(x < zero))) {
+        } else if (is_const_one(simplify(x < zero))) {
             return -1;
         }
     }

src/CSE.cpp

@@ -76,33 +76,23 @@ class GVN : public IRMutator {
         Expr expr;
         int use_count = 0;
         // All consumer Exprs for which this is the last child Expr.
-        map<ExprWithCompareCache, int> uses;
+        map<Expr, int, IRGraphDeepCompare> uses;
         Entry(const Expr &e)
             : expr(e) {
         }
     };
     vector<std::unique_ptr<Entry>> entries;
 
     map<Expr, int, ExprCompare> shallow_numbering, output_numbering;
-    map<ExprWithCompareCache, int> leaves;
+    map<Expr, int, IRGraphDeepCompare> leaves;
 
-    int number = -1;
-
-    IRCompareCache cache;
-
-    GVN()
-        : number(0), cache(8) {
-    }
+    int number = 0;
 
     Stmt mutate(const Stmt &s) override {
         internal_error << "Can't call GVN on a Stmt: " << s << "\n";
         return Stmt();
     }
 
-    ExprWithCompareCache with_cache(const Expr &e) {
-        return ExprWithCompareCache(e, &cache);
-    }
-
     Expr mutate(const Expr &e) override {
         // Early out if we've already seen this exact Expr.
         {
@@ -123,7 +113,7 @@ class GVN : public IRMutator {
         // that child has an identical parent to this one.
 
         auto &use_map = number == -1 ? leaves : entries[number]->uses;
-        auto p = use_map.emplace(with_cache(new_e), (int)entries.size());
+        auto p = use_map.emplace(new_e, (int)entries.size());
         auto iter = p.first;
         bool novel = p.second;
         if (novel) {