[lld-macho][nfc] Simplify MarkLive.cpp using `if constexpr`

No significant perf diff, as expected.

             base           diff           difference (95% CI)
  sys_time   1.722 ± 0.030  1.727 ± 0.027  [  -0.6% ..   +1.2%]
  user_time  5.081 ± 0.032  5.087 ± 0.030  [  -0.2% ..   +0.4%]
  wall_time  6.008 ± 0.056  6.029 ± 0.053  [  -0.1% ..   +0.8%]
  samples    25             37

Reviewed By: #lld-macho, oontvoo, thakis, BertalanD

Differential Revision: https://reviews.llvm.org/D133014

diff --git a/lld/MachO/MarkLive.cpp b/lld/MachO/MarkLive.cpp
index ba7d215..d407599 100644 (file)
--- a/lld/MachO/MarkLive.cpp
+++ b/lld/MachO/MarkLive.cpp
@@ -57,7 +57,6 @@ public:
 private:
   void enqueue(InputSection *isec, uint64_t off, const WorklistEntry *prev);
   void addSym(Symbol *s, const WorklistEntry *prev);
-  void printWhyLive(Symbol *s, const WorklistEntry *prev);
   const InputSection *getInputSection(const WorklistEntry *) const;
   WorklistEntry *makeEntry(InputSection *, const WorklistEntry *prev) const;
 
@@ -82,23 +81,7 @@ void MarkLiveImpl<RecordWhyLive>::enqueue(
   }
 }
 
-template <bool RecordWhyLive>
-void MarkLiveImpl<RecordWhyLive>::addSym(
-    Symbol *s,
-    const typename MarkLiveImpl<RecordWhyLive>::WorklistEntry *prev) {
-  if (s->used)
-    return;
-  s->used = true;
-  printWhyLive(s, prev);
-  if (auto *d = dyn_cast<Defined>(s)) {
-    if (d->isec)
-      enqueue(d->isec, d->value, prev);
-    if (d->unwindEntry)
-      enqueue(d->unwindEntry, 0, prev);
-  }
-}
-
-static void printWhyLiveImpl(const Symbol *s, const WhyLiveEntry *prev) {
+static void printWhyLive(const Symbol *s, const WhyLiveEntry *prev) {
   std::string out = toString(*s) + " from " + toString(s->getFile());
   int indent = 2;
   for (const WhyLiveEntry *entry = prev; entry;
@@ -113,44 +96,47 @@ static void printWhyLiveImpl(const Symbol *s, const WhyLiveEntry *prev) {
   message(out);
 }
 
-// NOTE: if/when `constexpr if` becomes available, we can simplify a lot of
-// the partial template specializations below.
-
-template <>
-void MarkLiveImpl<true>::printWhyLive(Symbol *s, const WhyLiveEntry *prev) {
-  if (!config->whyLive.empty() && config->whyLive.match(s->getName()))
-    printWhyLiveImpl(s, prev);
-}
-
-template <>
-void MarkLiveImpl<false>::printWhyLive(Symbol *s, const InputSection *prev) {}
-
-template <>
-const InputSection *
-MarkLiveImpl<true>::getInputSection(const WhyLiveEntry *entry) const {
-  return entry->isec;
+template <bool RecordWhyLive>
+void MarkLiveImpl<RecordWhyLive>::addSym(
+    Symbol *s,
+    const typename MarkLiveImpl<RecordWhyLive>::WorklistEntry *prev) {
+  if (s->used)
+    return;
+  s->used = true;
+  if constexpr (RecordWhyLive)
+    if (!config->whyLive.empty() && config->whyLive.match(s->getName()))
+      printWhyLive(s, prev);
+  if (auto *d = dyn_cast<Defined>(s)) {
+    if (d->isec)
+      enqueue(d->isec, d->value, prev);
+    if (d->unwindEntry)
+      enqueue(d->unwindEntry, 0, prev);
+  }
 }
 
-template <>
-const InputSection *
-MarkLiveImpl<false>::getInputSection(const InputSection *isec) const {
-  return isec;
+template <bool RecordWhyLive>
+const InputSection *MarkLiveImpl<RecordWhyLive>::getInputSection(
+    const MarkLiveImpl<RecordWhyLive>::WorklistEntry *entry) const {
+  if constexpr (RecordWhyLive)
+    return entry->isec;
+  else
+    return entry;
 }
 
-template <>
-typename MarkLiveImpl<true>::WorklistEntry *MarkLiveImpl<true>::makeEntry(
-    InputSection *isec, const MarkLiveImpl<true>::WorklistEntry *prev) const {
-  if (!isec) {
-    assert(!prev);
-    return nullptr;
+template <bool RecordWhyLive>
+typename MarkLiveImpl<RecordWhyLive>::WorklistEntry *
+MarkLiveImpl<RecordWhyLive>::makeEntry(
+    InputSection *isec,
+    const MarkLiveImpl<RecordWhyLive>::WorklistEntry *prev) const {
+  if constexpr (RecordWhyLive) {
+    if (!isec) {
+      assert(!prev);
+      return nullptr;
+    }
+    return make<WhyLiveEntry>(isec, prev);
+  } else {
+    return isec;
   }
-  return make<WhyLiveEntry>(isec, prev);
-}
-
-template <>
-typename MarkLiveImpl<false>::WorklistEntry *MarkLiveImpl<false>::makeEntry(
-    InputSection *isec, const MarkLiveImpl<false>::WorklistEntry *prev) const {
-  return isec;
 }
 
 template <bool RecordWhyLive>