return early if output arg is runtime inactive

enzyme/tools/enzyme-tblgen/blas-tblgen.cpp

@@ -1237,6 +1237,7 @@ void emit_rev_rewrite_rules(const StringMap<TGPattern> &patternMap,
   const auto rules = pattern.getRules();
   const auto activeArgs = pattern.getActiveArgs();
   const bool lv23 = pattern.isBLASLevel2or3();
+  const auto mutArgSet = pattern.getMutableArgs();
 
   // If any of the rule uses DiffeRet, the primary function has a ret val
   // and we should emit the code for handling it.
@@ -1323,6 +1324,30 @@ void emit_rev_rewrite_rules(const StringMap<TGPattern> &patternMap,
   }
   os << "  }\n";
 
+  // Blas functions return one float XOR modify one output arg.
+  // If we have runtimeActivity and the output arg is inactive,
+  // we don't need to do anything here and can return early.
+  if (mutArgSet.size() == 1) {
+    for (auto pos : mutArgSet) {
+      auto name = nameVec[pos];
+      os << "  Value *rt_inactive_out = rt_inactive_" << name << ";\n";
+      os << "  if (EnzymeRuntimeActivityCheck && cacheMode) {\n"
+         << "    BasicBlock *current = Builder2.GetInsertBlock();\n"
+         << "    auto bb_name = Builder2.GetInsertBlock()->getName();\n"
+         << "    auto earlyRetBlock = gutils->addReverseBlock(current, bb_name "
+            "+ \".early.return\");\n"
+         << "    auto continueBlock = gutils->addReverseBlock(earlyRetBlock, "
+            "bb_name + \".continue\");\n"
+         << "    Builder2.CreateCondBr(rt_inactive_out, earlyRetBlock, "
+            "continueBlock);\n"
+         << "    Builder2.SetInsertPoint(earlyRetBlock);\n"
+         << "    Builder2.CreateRetVoid();\n"
+         << "    Builder2.SetInsertPoint(continueBlock);\n"
+         << "  }\n";
+      break;
+    }
+  }
+
   // now we can use it to transpose our trans arguments if they exist
   for (size_t i = (lv23 ? 1 : 0); i < nameVec.size(); i++) {
     auto name = nameVec[i];