From f21774f3865e506b6dea912af8f8be16fd29dacb Mon Sep 17 00:00:00 2001
From: Alon Zakai <azakai@google.com>
Date: Fri, 27 May 2022 11:16:39 -0700
Subject: OptimizeInstructions: Turn call_ref of a select into an if over two
 direct calls  (#4660)

This extends the existing call_indirect code to do the same for call_ref,
basically. The shared code is added to a new helper utility.
---
 src/passes/Directize.cpp | 115 ++++++++++++++++++++---------------------------
 1 file changed, 48 insertions(+), 67 deletions(-)

(limited to 'src/passes/Directize.cpp')

diff --git a/src/passes/Directize.cpp b/src/passes/Directize.cpp
index 6853f1faf..e338272a9 100644
--- a/src/passes/Directize.cpp
+++ b/src/passes/Directize.cpp
@@ -22,6 +22,7 @@
 
 #include <unordered_map>
 
+#include "call-utils.h"
 #include "ir/table-utils.h"
 #include "ir/type-updating.h"
 #include "ir/utils.h"
@@ -59,62 +60,19 @@ struct FunctionDirectizer : public WalkerPass<PostWalker<FunctionDirectizer>> {
       return;
     }
 
-    // If the target is a select of two different constants, we can emit two
-    // direct calls.
-    // TODO: handle 3+
-    // TODO: handle the case where just one arm is a constant?
-    if (auto* select = curr->target->dynCast<Select>()) {
-      if (select->ifTrue->is<Const>() && select->ifFalse->is<Const>()) {
-        Builder builder(*getModule());
-        auto* func = getFunction();
-        std::vector<Expression*> blockContents;
-
-        if (select->condition->type == Type::unreachable) {
-          // Leave this for DCE.
-          return;
-        }
-
-        // We must use the operands twice, and also must move the condition to
-        // execute first; use locals for them all. While doing so, if we see
-        // any are unreachable, stop trying to optimize and leave this for DCE.
-        std::vector<Index> operandLocals;
-        for (auto* operand : curr->operands) {
-          if (operand->type == Type::unreachable ||
-              !TypeUpdating::canHandleAsLocal(operand->type)) {
-            return;
-          }
-        }
-
-        // None of the types are a problem, so we can proceed to add new vars as
-        // needed and perform this optimization.
-        for (auto* operand : curr->operands) {
-          auto currLocal = builder.addVar(func, operand->type);
-          operandLocals.push_back(currLocal);
-          blockContents.push_back(builder.makeLocalSet(currLocal, operand));
-          // By adding locals we must make type adjustments at the end.
-          changedTypes = true;
-        }
-
-        // Build the calls.
-        auto numOperands = curr->operands.size();
-        auto getOperands = [&]() {
-          std::vector<Expression*> newOperands(numOperands);
-          for (Index i = 0; i < numOperands; i++) {
-            newOperands[i] =
-              builder.makeLocalGet(operandLocals[i], curr->operands[i]->type);
-          }
-          return newOperands;
-        };
-        auto* ifTrueCall =
-          makeDirectCall(getOperands(), select->ifTrue, flatTable, curr);
-        auto* ifFalseCall =
-          makeDirectCall(getOperands(), select->ifFalse, flatTable, curr);
-
-        // Create the if to pick the calls, and emit the final block.
-        auto* iff = builder.makeIf(select->condition, ifTrueCall, ifFalseCall);
-        blockContents.push_back(iff);
-        replaceCurrent(builder.makeBlock(blockContents));
-      }
+    // Emit direct calls for things like a select over constants.
+    if (auto* calls = CallUtils::convertToDirectCalls(
+          curr,
+          [&](Expression* target) {
+            return getTargetInfo(target, flatTable, curr);
+          },
+          *getFunction(),
+          *getModule())) {
+      replaceCurrent(calls);
+      // Note that types may have changed, as the utility here can add locals
+      // which require fixups if they are non-nullable, for example.
+      changedTypes = true;
+      return;
     }
   }
 
@@ -131,6 +89,36 @@ private:
 
   bool changedTypes = false;
 
+  // Given an expression that we will use as the target of an indirect call,
+  // analyze it and return one of the results of CallUtils::IndirectCallInfo,
+  // that is, whether we know a direct call target, or we know it will trap, or
+  // if we know nothing.
+  CallUtils::IndirectCallInfo
+  getTargetInfo(Expression* target,
+                const TableUtils::FlatTable& flatTable,
+                CallIndirect* original) {
+    auto* c = target->dynCast<Const>();
+    if (!c) {
+      return CallUtils::Unknown{};
+    }
+
+    Index index = c->value.geti32();
+
+    // If the index is invalid, or the type is wrong, then this will trap.
+    if (index >= flatTable.names.size()) {
+      return CallUtils::Trap{};
+    }
+    auto name = flatTable.names[index];
+    if (!name.is()) {
+      return CallUtils::Trap{};
+    }
+    auto* func = getModule()->getFunction(name);
+    if (original->heapType != func->type) {
+      return CallUtils::Trap{};
+    }
+    return CallUtils::Known{name};
+  }
+
   // Create a direct call for a given list of operands, an expression which is
   // known to contain a constant indicating the table offset, and the relevant
   // table. If we can see that the call will trap, instead return an
@@ -139,23 +127,16 @@ private:
                              Expression* c,
                              const TableUtils::FlatTable& flatTable,
                              CallIndirect* original) {
-    Index index = c->cast<Const>()->value.geti32();
-
     // If the index is invalid, or the type is wrong, we can
     // emit an unreachable here, since in Binaryen it is ok to
     // reorder/replace traps when optimizing (but never to
     // remove them, at least not by default).
-    if (index >= flatTable.names.size()) {
-      return replaceWithUnreachable(operands);
-    }
-    auto name = flatTable.names[index];
-    if (!name.is()) {
-      return replaceWithUnreachable(operands);
-    }
-    auto* func = getModule()->getFunction(name);
-    if (original->heapType != func->type) {
+    auto info = getTargetInfo(c, flatTable, original);
+    if (std::get_if<CallUtils::Trap>(&info)) {
       return replaceWithUnreachable(operands);
     }
+    assert(std::get_if<CallUtils::Known>(&info));
+    auto name = std::get_if<CallUtils::Known>(&info)->target;
 
     // Everything looks good!
     return Builder(*getModule())
-- 
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