Z: Replace Thread.onSpinWait() with a nop instruction

Accelerate inlining Thread.onSpinWait() on z. Thread.onSpinWait() is a simple `nop` instruction on z. Enabled by default. Disable by setting the `TR_noPauseOnSpinWait` environment variable. Signed-off-by: Ehsan Kiani Far <[email protected]>
eclipse-openj9 · Nov 22, 2024 · 077f69f · 077f69f
1 parent ff43532
commit 077f69f
Show file tree

Hide file tree

Showing 3 changed files with 34 additions and 0 deletions.
diff --git a/runtime/compiler/z/codegen/J9CodeGenerator.cpp b/runtime/compiler/z/codegen/J9CodeGenerator.cpp
@@ -4043,6 +4043,14 @@ J9::Z::CodeGenerator::inlineDirectCall(
             return resultReg != NULL;
             }
          break;
+      case TR::java_lang_Thread_onSpinWait:
+         static char *disableOSW = feGetEnv("TR_noPauseOnSpinWait");
+         if (!disableOSW)
+            {
+            resultReg = TR::TreeEvaluator::inlineOnSpinWait(node, cg);
+            return true;
+            }
+         break;
 
       default:
          break;

diff --git a/runtime/compiler/z/codegen/J9TreeEvaluator.cpp b/runtime/compiler/z/codegen/J9TreeEvaluator.cpp
@@ -14665,3 +14665,15 @@ J9::Z::TreeEvaluator::inlineIntegerStringSize(TR::Node* node, TR::CodeGenerator*
 
    return node->setRegister(lengthReg);
    }
+
+TR::Register*
+J9::Z::TreeEvaluator::inlineOnSpinWait(TR::Node *node, TR::CodeGenerator *cg) {
+   // Thread.onSpinWait() on z is a simple "nop" instruction.
+   cg->generateNop(node);
+   static const bool printIt = feGetEnv("TR_showPauseOnSpinWait") != NULL;
+   if (printIt && comp->getOption(TR_TraceCG))
+      {
+      traceMsg(comp, "insert PAUSE for onSpinWait : node=%p, %s\n", node, comp->signature());
+      }
+   return NULL;
+}
diff --git a/runtime/compiler/z/codegen/J9TreeEvaluator.hpp b/runtime/compiler/z/codegen/J9TreeEvaluator.hpp
@@ -141,6 +141,20 @@ class OMR_EXTENSIBLE TreeEvaluator: public J9::TreeEvaluator
    static TR::Register* inlineUTF16BEEncode    (TR::Node *node, TR::CodeGenerator *cg);
    static TR::Register *inlineCRC32CUpdateBytes(TR::Node *node, TR::CodeGenerator *cg, bool isDirectBuffer);
 
+      /**
+    * \brief
+    *
+    * Accelerate inlining onSpinWait() method.
+    *
+    * \details
+    *
+    * \param node the method call node.
+    * \param cg the code generator.
+    *
+    * \return NULL.
+    */
+   static TR::Register *inlineOnSpinWait(TR::Node *node, TR::CodeGenerator *cg);
+
    static TR::Register *zdloadEvaluator(TR::Node *node, TR::CodeGenerator *cg);
    static TR::Register *zdloadiEvaluator(TR::Node *node, TR::CodeGenerator *cg);
    static TR::Register *zdstoreEvaluator(TR::Node *node, TR::CodeGenerator *cg);