1 files changed, 104 insertions, 0 deletions
diff --git a/js/src/jit/FoldLinearArithConstants.cpp b/js/src/jit/FoldLinearArithConstants.cpp
new file mode 100644
index 000000000..b97720cec
--- /dev/null
+++ b/js/src/jit/FoldLinearArithConstants.cpp
@@ -0,0 +1,104 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "jit/FoldLinearArithConstants.h"
+
+#include "jit/IonAnalysis.h"
+#include "jit/MIR.h"
+#include "jit/MIRGenerator.h"
+#include "jit/MIRGraph.h"
+
+using namespace js;
+using namespace jit;
+
+namespace js {
+namespace jit {
+
+// Mark this node and its children as RecoveredOnBailout when they are not used.
+// The marked nodes will be removed during DCE. Marking as RecoveredOnBailout is
+// necessary because the Sink pass is ran before this pass.
+static void
+markNodesAsRecoveredOnBailout(MDefinition* def)
+{
+    if (def->hasLiveDefUses() || !DeadIfUnused(def) || !def->canRecoverOnBailout())
+        return;
+
+    JitSpew(JitSpew_FLAC, "mark as recovered on bailout: %s%u", def->opName(), def->id());
+    def->setRecoveredOnBailoutUnchecked();
+
+    // Recursively mark nodes that do not have multiple uses. This loop is
+    // necessary because a node could be an unused right shift zero or an
+    // unused add, and both need to be marked as RecoveredOnBailout.
+    for (size_t i = 0; i < def->numOperands(); i++)
+        markNodesAsRecoveredOnBailout(def->getOperand(i));
+}
+
+// Fold AddIs with one variable and two or more constants into one AddI.
+static void
+AnalyzeAdd(TempAllocator& alloc, MAdd* add)
+{
+    if (add->specialization() != MIRType::Int32 || add->isRecoveredOnBailout())
+        return;
+
+    if (!add->hasUses())
+        return;
+
+    JitSpew(JitSpew_FLAC, "analyze add: %s%u", add->opName(), add->id());
+
+    SimpleLinearSum sum = ExtractLinearSum(add);
+    if (sum.constant == 0 || !sum.term)
+        return;
+
+    // Determine which operand is the constant.
+    int idx = add->getOperand(0)->isConstant() ? 0 : 1 ;
+    if (add->getOperand(idx)->isConstant()) {
+        // Do not replace an add where the outcome is the same add instruction.
+        MOZ_ASSERT(add->getOperand(idx)->toConstant()->type() == MIRType::Int32);
+        if (sum.term == add->getOperand(1 - idx) ||
+            sum.constant == add->getOperand(idx)->toConstant()->toInt32())
+        {
+            return;
+        }
+    }
+
+    MInstruction* rhs = MConstant::New(alloc, Int32Value(sum.constant));
+    add->block()->insertBefore(add, rhs);
+
+    MAdd* addNew = MAdd::New(alloc, sum.term, rhs, MIRType::Int32);
+
+    add->replaceAllLiveUsesWith(addNew);
+    add->block()->insertBefore(add, addNew);
+    JitSpew(JitSpew_FLAC, "replaced with: %s%u", addNew->opName(), addNew->id());
+    JitSpew(JitSpew_FLAC, "and constant: %s%u (%d)", rhs->opName(), rhs->id(), sum.constant);
+
+    // Mark the stale nodes as RecoveredOnBailout since the Sink pass has
+    // been run before this pass. DCE will then remove the unused nodes.
+    markNodesAsRecoveredOnBailout(add);
+}
+
+bool
+FoldLinearArithConstants(MIRGenerator* mir, MIRGraph& graph)
+{
+    for (PostorderIterator block(graph.poBegin()); block != graph.poEnd(); block++) {
+        if (mir->shouldCancel("Fold Linear Arithmetic Constants (main loop)"))
+            return false;
+
+        for (MInstructionIterator i = block->begin(); i != block->end(); i++) {
+            if (!graph.alloc().ensureBallast())
+                return false;
+
+            if (mir->shouldCancel("Fold Linear Arithmetic Constants (inner loop)"))
+                return false;
+
+            if (i->isAdd())
+                AnalyzeAdd(graph.alloc(), i->toAdd());
+        }
+    }
+    return true;
+}
+
+} /* namespace jit */
+} /* namespace js */