rewriter: remove duplicate getAttr calls

src/asm_writing/rewriter.cpp

@@ -416,6 +416,20 @@ void Rewriter::_addAttrGuard(RewriterVar* var, int offset, RewriterVar* val_cons
 RewriterVar* RewriterVar::getAttr(int offset, Location dest, assembler::MovType type) {
     STAT_TIMER(t0, "us_timer_rewriter", 10);
 
+    // if no changing action happened we can reuse get attributes
+    if (!rewriter->added_changing_action) {
+        RewriterVar*& result = getattrs[std::make_pair(offset, (int)type)];
+        if (result) {
+            if (dest != Location::any())
+                result->getInReg(dest, true /* allow_constant_in_reg */);
+        } else {
+            result = rewriter->createNewVar();
+            rewriter->addAction([=]() { rewriter->_getAttr(result, this, offset, dest, type); }, { this },
+                                ActionType::NORMAL);
+        }
+        return result;
+    }
+
     RewriterVar* result = rewriter->createNewVar();
     rewriter->addAction([=]() { rewriter->_getAttr(result, this, offset, dest, type); }, { this }, ActionType::NORMAL);
     return result;

src/asm_writing/rewriter.h

@@ -263,7 +263,8 @@ private:
     Location arg_loc;
     std::pair<int /*offset*/, int /*size*/> scratch_allocation;
 
-    llvm::SmallSet<std::tuple<int, uint64_t, bool>, 4> attr_guards; // used to detect duplicate guards
+    llvm::SmallSet<std::tuple<int, uint64_t, bool>, 4> attr_guards;  // used to detect duplicate guards
+    llvm::SmallDenseMap<std::pair<int, int>, RewriterVar*> getattrs; // used to detect duplicate getAttrs
 
     // Gets a copy of this variable in a register, spilling/reloading if necessary.
     // TODO have to be careful with the result since the interface doesn't guarantee

src/codegen/baseline_jit.cpp

@@ -177,6 +177,8 @@ JitFragmentWriter::JitFragmentWriter(CFGBlock* block, std::unique_ptr<ICInfo> ic
       ic_info(std::move(ic_info)) {
     allocatable_regs = bjit_allocatable_regs;
 
+    added_changing_action = true;
+
     if (LOG_BJIT_ASSEMBLY)
         comment("BJIT: JitFragmentWriter() start");
     interp = createNewVar();