[NFC] Move value numbering code to a header

src/ir/numbering.h

@@ -0,0 +1,67 @@
+/*
+ * Copyright 2021 WebAssembly Community Group participants
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef wasm_ir_numberings_h
+#define wasm_ir_numberings_h
+
+#include "wasm.h"
+
+namespace wasm {
+
+// General value numbering: Returns a number for an expression. Expressions with
+// the same number must be identical in value; expressions with different values
+// might happen to be identical at runtime.
+class ValueNumbering {
+public:
+  // Get the value numbering of an arbitrary expression.
+  Index getValue(Expression* expr) {
+    if (Properties::isConstantExpression(expr)) {
+      return getValue(Properties::getLiterals(expr));
+    } else {
+      auto iter = expressionValues.find(expr);
+      if (iter != expressionValues.end()) {
+        return iter->second;
+      }
+      // TODO: full GVN to check for different expressions with the same value.
+      return expressionValues[expr] = getUniqueValue();
+    }
+  }
+
+  // Get the value numbering of an arbitrary set of constants.
+  Index getValue(Literals lit) {
+    auto iter = literalValues.find(lit);
+    if (iter != literalValues.end()) {
+      return iter->second;
+    }
+    return literalValues[lit] = getUniqueValue();
+  }
+
+  // Return a new unique value. Normally this is called internally, but there
+  // are also use cases for the user of the class to call this, when they want
+  // to get a new value that will not collide with any others.
+  Index getUniqueValue() { return nextValue++; }
+
+private:
+  Index nextValue = 0;
+
+  // Cache the value numbers of literals and expressions.
+  std::unordered_map<Literals, Index> literalValues;
+  std::unordered_map<Expression*, Index> expressionValues;
+};
+
+} // namespace wasm
+
+#endif // wasm_ir_numberings_h

src/passes/RedundantSetElimination.cpp

@@ -35,6 +35,7 @@
 
 #include <cfg/cfg-traversal.h>
 #include <ir/literal-utils.h>
+#include <ir/numbering.h>
 #include <ir/properties.h>
 #include <ir/utils.h>
 #include <pass.h>
@@ -44,11 +45,9 @@
 
 namespace wasm {
 
-// We do a very simple numbering of local values, just a unique
-// number for constants so far, enough to see
-// trivial duplication. LocalValues maps each local index to
-// its current value
-typedef std::vector<Index> LocalValues;
+// Map each local index to its current value number (which is computed in
+// ValueNumbering).
+using LocalValues = std::vector<Index>;
 
 namespace {
 
@@ -84,6 +83,10 @@ struct RedundantSetElimination
     if (numLocals == 0) {
       return; // nothing to do
     }
+
+    // Create a unique value for use to mark unseen locations.
+    unseenValue = valueNumbering.getUniqueValue();
+
     // create the CFG by walking the IR
     CFGWalker<RedundantSetElimination, Visitor<RedundantSetElimination>, Info>::
       doWalkFunction(func);
@@ -93,47 +96,30 @@ struct RedundantSetElimination
     optimize();
   }
 
-  // numbering
+  // Use a value numbering for the values of expressions.
+  ValueNumbering valueNumbering;
 
-  Index nextValue = 1; // 0 is reserved for the "unseen value"
-  // each constant has a value
-  std::unordered_map<Literals, Index> literalValues;
-  // each value can have a value
-  std::unordered_map<Expression*, Index> expressionValues;
-  // each block has values for each merge
+  // In additon to valueNumbering, each block has values for each merge.
   std::unordered_map<BasicBlock*, std::unordered_map<Index, Index>>
     blockMergeValues;
 
-  Index getUnseenValue() { // we haven't seen this location yet
-    return 0;
-  }
-  Index getUniqueValue() {
-#ifdef RSE_DEBUG
-    std::cout << "new unique value " << nextValue << '\n';
-#endif
-    return nextValue++;
-  }
+  // A value that indicates we haven't seen this location yet.
+  Index unseenValue;
 
-  Index getLiteralValue(Literals lit) {
-    auto iter = literalValues.find(lit);
-    if (iter != literalValues.end()) {
-      return iter->second;
-    }
+  Index getUniqueValue() {
+    auto value = valueNumbering.getUniqueValue();
 #ifdef RSE_DEBUG
-    std::cout << "new literal value for " << lit << '\n';
+    std::cout << "new unique value " << value << '\n';
 #endif
-    return literalValues[lit] = getUniqueValue();
+    return value;
   }
 
-  Index getExpressionValue(Expression* expr) {
-    auto iter = expressionValues.find(expr);
-    if (iter != expressionValues.end()) {
-      return iter->second;
-    }
+  Index getValue(Literals lit) {
+    auto value = valueNumbering.getValue(lit);
 #ifdef RSE_DEBUG
-    std::cout << "new expr value for " << expr << '\n';
+    std::cout << "lit value " << value << '\n';
 #endif
-    return expressionValues[expr] = getUniqueValue();
+    return value;
   }
 
   Index getBlockMergeValue(BasicBlock* block, Index index) {
@@ -162,17 +148,16 @@ struct RedundantSetElimination
     return value == iter2->second;
   }
 
-  Index getValue(Expression* value, LocalValues& currValues) {
-    if (Properties::isConstantExpression(value)) {
-      // a constant
-      return getLiteralValue(Properties::getLiterals(value));
-    } else if (auto* get = value->dynCast<LocalGet>()) {
+  Index getValue(Expression* expr, LocalValues& currValues) {
+    if (auto* get = expr->dynCast<LocalGet>()) {
       // a copy of whatever that was
       return currValues[get->index];
-    } else {
-      // get the value's own unique value
-      return getExpressionValue(value);
     }
+    auto value = valueNumbering.getValue(expr);
+#ifdef RSE_DEBUG
+    std::cout << "expr value " << value << '\n';
+#endif
+    return value;
   }
 
   // flowing
@@ -196,20 +181,20 @@ struct RedundantSetElimination
 #endif
             start[i] = getUniqueValue();
           } else {
-            start[i] = getLiteralValue(Literal::makeZeros(type));
+            start[i] = getValue(Literal::makeZeros(type));
           }
         }
       } else {
         // other blocks have all unseen values to begin with
         for (Index i = 0; i < numLocals; i++) {
-          start[i] = getUnseenValue();
+          start[i] = unseenValue;
         }
       }
       // the ends all begin unseen
       LocalValues& end = block->contents.end;
       end.resize(numLocals);
       for (Index i = 0; i < numLocals; i++) {
-        end[i] = getUnseenValue();
+        end[i] = unseenValue;
       }
     }
     // keep working while stuff is flowing. we use a unique deferred queue
@@ -280,9 +265,9 @@ struct RedundantSetElimination
             iter++;
             while (iter != in.end()) {
               auto otherValue = (*iter)->contents.end[i];
-              if (value == getUnseenValue()) {
+              if (value == unseenValue) {
                 value = otherValue;
-              } else if (otherValue == getUnseenValue()) {
+              } else if (otherValue == unseenValue) {
                 // nothing to do, other has no information
               } else if (value != otherValue) {
                 // 2 different values, this is a merged value