commit 18c346c5230f970b600516ac44957914036973c2
author benjamin@webkit.org <benjamin@webkit.org@268f45cc-cd09-0410-ab3c-d52691b4dbfc> Wed Mar 02 07:53:20 2016 +0000
committer benjamin@webkit.org <benjamin@webkit.org@268f45cc-cd09-0410-ab3c-d52691b4dbfc> Wed Mar 02 07:53:20 2016 +0000
tree 2d43d6df0096e026a3c7d81efb87cb62f97f3b39
parent 1e0e32fc8803745b8c8f6b441bf3298b1affac65

[JSC] Simplify ArithMod(ArithMod(x, const1), const2) if const2 >= const1
https://bugs.webkit.org/show_bug.cgi?id=154904

Reviewed by Saam Barati.

The ASM test "ubench" has a "x % 10 % 255".
The second modulo should be eliminated.

This is a 15% improvement on ASMJS' ubench.

* dfg/DFGStrengthReductionPhase.cpp:
(JSC::DFG::StrengthReductionPhase::handleNode):
* tests/stress/arith-modulo-twice.js: Added.
(opaqueModuloSmaller):
(opaqueModuloEqual):
(opaqueModuloLarger):
(opaqueModuloSmallerNeg):
(opaqueModuloEqualNeg):
(opaqueModuloLargerNeg):
(opaqueExpectedOther):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@197445 268f45cc-cd09-0410-ab3c-d52691b4dbfc

Source/JavaScriptCore/dfg/DFGStrengthReductionPhase.cpp

diff --git a/Source/JavaScriptCore/dfg/DFGStrengthReductionPhase.cpp b/Source/JavaScriptCore/dfg/DFGStrengthReductionPhase.cpp
index 14ad79e..acfad65 100644
--- a/Source/JavaScriptCore/dfg/DFGStrengthReductionPhase.cpp
+++ b/Source/JavaScriptCore/dfg/DFGStrengthReductionPhase.cpp
@@ -36,6 +36,7 @@
 #include "DFGPredictionPropagationPhase.h"
 #include "DFGVariableAccessDataDump.h"
 #include "JSCInlines.h"
+#include <cstdlib>
 
 namespace JSC { namespace DFG {
 
@@ -172,6 +173,21 @@
             }
             break;
 
+        case ArithMod:
+            // On Integers
+            // In: ArithMod(ArithMod(x, const1), const2)
+            // Out: Identity(ArithMod(x, const1))
+            //     if const1 <= const2.
+            if (m_node->binaryUseKind() == Int32Use
+                && m_node->child2()->isInt32Constant()
+                && m_node->child1()->op() == ArithMod
+                && m_node->child1()->binaryUseKind() == Int32Use
+                && m_node->child1()->child2()->isInt32Constant()
+                && std::abs(m_node->child1()->child2()->asInt32()) <= std::abs(m_node->child2()->asInt32())) {
+                    convertToIdentityOverChild1();
+            }
+            break;
+
         case ValueRep:
         case Int52Rep:
         case DoubleRep: {