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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/214926">214926</a></dd>
<dt>Author</dt> <dd>fpizlo@apple.com</dd>
<dt>Date</dt> <dd>2017-04-04 20:43:44 -0700 (Tue, 04 Apr 2017)</dd>
</dl>
<h3>Log Message</h3>
<pre>Air::eliminateDeadCode should not repeatedly process the same live instructions
https://bugs.webkit.org/show_bug.cgi?id=170490
Reviewed by Keith Miller.
This makes the eliminateDeadCode() fixpoint somewhat worklist-based: we track the set
of Insts that might be dead. Every time we detect that one is live, we remove it from
the set. This is a big (>2x) speed-up because lots of Insts are immediately found to
be live.
This is a ~1% wasm -O1 compile time progression.
* b3/air/AirEliminateDeadCode.cpp:
(JSC::B3::Air::eliminateDeadCode):</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceJavaScriptCoreChangeLog">trunk/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCoreb3airAirEliminateDeadCodecpp">trunk/Source/JavaScriptCore/b3/air/AirEliminateDeadCode.cpp</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/ChangeLog (214925 => 214926)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/ChangeLog 2017-04-05 03:26:03 UTC (rev 214925)
+++ trunk/Source/JavaScriptCore/ChangeLog 2017-04-05 03:43:44 UTC (rev 214926)
</span><span class="lines">@@ -1,5 +1,22 @@
</span><span class="cx"> 2017-04-04 Filip Pizlo <fpizlo@apple.com>
</span><span class="cx">
</span><ins>+ Air::eliminateDeadCode should not repeatedly process the same live instructions
+ https://bugs.webkit.org/show_bug.cgi?id=170490
+
+ Reviewed by Keith Miller.
+
+ This makes the eliminateDeadCode() fixpoint somewhat worklist-based: we track the set
+ of Insts that might be dead. Every time we detect that one is live, we remove it from
+ the set. This is a big (>2x) speed-up because lots of Insts are immediately found to
+ be live.
+
+ This is a ~1% wasm -O1 compile time progression.
+
+ * b3/air/AirEliminateDeadCode.cpp:
+ (JSC::B3::Air::eliminateDeadCode):
+
+2017-04-04 Filip Pizlo <fpizlo@apple.com>
+
</ins><span class="cx"> Air::eliminateDeadCode() should not use a HashSet
</span><span class="cx"> https://bugs.webkit.org/show_bug.cgi?id=170487
</span><span class="cx">
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreb3airAirEliminateDeadCodecpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/b3/air/AirEliminateDeadCode.cpp (214925 => 214926)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/b3/air/AirEliminateDeadCode.cpp 2017-04-05 03:26:03 UTC (rev 214925)
+++ trunk/Source/JavaScriptCore/b3/air/AirEliminateDeadCode.cpp 2017-04-05 03:43:44 UTC (rev 214926)
</span><span class="lines">@@ -44,7 +44,7 @@
</span><span class="cx"> TmpSet liveTmps;
</span><span class="cx"> IndexSet<StackSlot*> liveStackSlots;
</span><span class="cx"> bool changed;
</span><del>-
</del><ins>+
</ins><span class="cx"> auto isArgLive = [&] (const Arg& arg) -> bool {
</span><span class="cx"> switch (arg.kind()) {
</span><span class="cx"> case Arg::Tmp:
</span><span class="lines">@@ -60,21 +60,6 @@
</span><span class="cx"> }
</span><span class="cx"> };
</span><span class="cx">
</span><del>- auto addLiveArg = [&] (const Arg& arg) -> bool {
- switch (arg.kind()) {
- case Arg::Tmp:
- if (arg.isReg())
- return false;
- return liveTmps.add(arg.tmp());
- case Arg::Stack:
- if (arg.stackSlot()->isLocked())
- return false;
- return liveStackSlots.add(arg.stackSlot());
- default:
- return false;
- }
- };
-
</del><span class="cx"> auto isInstLive = [&] (Inst& inst) -> bool {
</span><span class="cx"> if (inst.hasNonArgEffects())
</span><span class="cx"> return true;
</span><span class="lines">@@ -91,39 +76,55 @@
</span><span class="cx"> });
</span><span class="cx"> return storesToLive;
</span><span class="cx"> };
</span><del>-
- auto handleInst = [&] (Inst& inst) {
</del><ins>+
+ // Returns true if it's live.
+ auto handleInst = [&] (Inst& inst) -> bool {
</ins><span class="cx"> if (!isInstLive(inst))
</span><del>- return;
</del><ins>+ return false;
</ins><span class="cx">
</span><span class="cx"> // We get here if the Inst is live. For simplicity we say that a live instruction forces
</span><span class="cx"> // liveness upon everything it mentions.
</span><span class="cx"> for (Arg& arg : inst.args) {
</span><del>- changed |= addLiveArg(arg);
</del><ins>+ if (arg.isStack() && !arg.stackSlot()->isLocked())
+ changed |= liveStackSlots.add(arg.stackSlot());
</ins><span class="cx"> arg.forEachTmpFast(
</span><span class="cx"> [&] (Tmp& tmp) {
</span><del>- changed |= addLiveArg(tmp);
</del><ins>+ if (!tmp.isReg())
+ changed |= liveTmps.add(tmp);
</ins><span class="cx"> });
</span><span class="cx"> }
</span><ins>+ return true;
</ins><span class="cx"> };
</span><span class="cx">
</span><ins>+ Vector<Inst*> possiblyDead;
+
+ for (BasicBlock* block : code) {
+ for (Inst& inst : *block) {
+ if (!handleInst(inst))
+ possiblyDead.append(&inst);
+ }
+ }
+
</ins><span class="cx"> auto runForward = [&] () -> bool {
</span><span class="cx"> changed = false;
</span><del>- for (BasicBlock* block : code) {
- for (Inst& inst : *block)
- handleInst(inst);
- }
</del><ins>+ possiblyDead.removeAllMatching(
+ [&] (Inst* inst) -> bool {
+ bool result = handleInst(*inst);
+ changed |= result;
+ return result;
+ });
</ins><span class="cx"> return changed;
</span><span class="cx"> };
</span><span class="cx">
</span><span class="cx"> auto runBackward = [&] () -> bool {
</span><span class="cx"> changed = false;
</span><del>- for (unsigned blockIndex = code.size(); blockIndex--;) {
- BasicBlock* block = code[blockIndex];
- if (!block)
- continue;
- for (unsigned instIndex = block->size(); instIndex--;)
- handleInst(block->at(instIndex));
</del><ins>+ for (unsigned i = possiblyDead.size(); i--;) {
+ bool result = handleInst(*possiblyDead[i]);
+ if (result) {
+ possiblyDead[i] = possiblyDead.last();
+ possiblyDead.removeLast();
+ changed = true;
+ }
</ins><span class="cx"> }
</span><span class="cx"> return changed;
</span><span class="cx"> };
</span></span></pre>
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