[lld] e0612c9 - [ELF] Optimize getInputSections. NFC

[Fangrui Song via llvm-commits]

Author: Fangrui Song
Date: 2022-07-05T23:31:09-07:00
New Revision: e0612c91cd16596ffa307952b1a8345c145f9326

URL: https://github.com/llvm/llvm-project/commit/e0612c91cd16596ffa307952b1a8345c145f9326
DIFF: https://github.com/llvm/llvm-project/commit/e0612c91cd16596ffa307952b1a8345c145f9326.diff

LOG: [ELF] Optimize getInputSections. NFC

In the majority of cases (e.g. orphan sections), an OutputSection has at most
one InputSectionDescription (isd). By changing the return type to
ArrayRef<InputSection *> we can just reference the isd->sections. For
OutputSections with more than one InputSectionDescription we use a caller
provided SmallVector to copy the elements as before.

Reviewed By: peter.smith

Differential Revision: https://reviews.llvm.org/D129111

Added: 
    

Modified: 
    lld/ELF/OutputSections.cpp
    lld/ELF/OutputSections.h
    lld/ELF/Writer.cpp

Removed: 
    


################################################################################
diff  --git a/lld/ELF/OutputSections.cpp b/lld/ELF/OutputSections.cpp
index bc940c7e6546..cbde8ac800d3 100644
--- a/lld/ELF/OutputSections.cpp
+++ b/lld/ELF/OutputSections.cpp
@@ -419,7 +419,8 @@ template <class ELFT> void OutputSection::writeTo(uint8_t *buf) {
   }
 
   // Write leading padding.
-  SmallVector<InputSection *, 0> sections = getInputSections(*this);
+  SmallVector<InputSection *, 0> storage;
+  ArrayRef<InputSection *> sections = getInputSections(*this, storage);
   std::array<uint8_t, 4> filler = getFiller();
   bool nonZeroFiller = read32(filler.data()) != 0;
   if (nonZeroFiller)
@@ -592,12 +593,24 @@ InputSection *elf::getFirstInputSection(const OutputSection *os) {
   return nullptr;
 }
 
-SmallVector<InputSection *, 0> elf::getInputSections(const OutputSection &os) {
-  SmallVector<InputSection *, 0> ret;
-  for (SectionCommand *cmd : os.commands)
-    if (auto *isd = dyn_cast<InputSectionDescription>(cmd))
-      ret.insert(ret.end(), isd->sections.begin(), isd->sections.end());
-  return ret;
+ArrayRef<InputSection *>
+elf::getInputSections(const OutputSection &os,
+                      SmallVector<InputSection *, 0> &storage) {
+  ArrayRef<InputSection *> ret;
+  storage.clear();
+  for (SectionCommand *cmd : os.commands) {
+    auto *isd = dyn_cast<InputSectionDescription>(cmd);
+    if (!isd)
+      continue;
+    if (ret.empty()) {
+      ret = isd->sections;
+    } else {
+      if (storage.empty())
+        storage.assign(ret.begin(), ret.end());
+      storage.insert(storage.end(), isd->sections.begin(), isd->sections.end());
+    }
+  }
+  return storage.empty() ? ret : makeArrayRef(storage);
 }
 
 // Sorts input sections by section name suffixes, so that .foo.N comes
@@ -622,7 +635,8 @@ std::array<uint8_t, 4> OutputSection::getFiller() {
 void OutputSection::checkDynRelAddends(const uint8_t *bufStart) {
   assert(config->writeAddends && config->checkDynamicRelocs);
   assert(type == SHT_REL || type == SHT_RELA);
-  SmallVector<InputSection *, 0> sections = getInputSections(*this);
+  SmallVector<InputSection *, 0> storage;
+  ArrayRef<InputSection *> sections = getInputSections(*this, storage);
   parallelFor(0, sections.size(), [&](size_t i) {
     // When linking with -r or --emit-relocs we might also call this function
     // for input .rel[a].<sec> sections which we simply pass through to the

diff  --git a/lld/ELF/OutputSections.h b/lld/ELF/OutputSections.h
index 020eeaec368e..6bdbcfce7b12 100644
--- a/lld/ELF/OutputSections.h
+++ b/lld/ELF/OutputSections.h
@@ -134,7 +134,9 @@ struct OutputDesc final : SectionCommand {
 int getPriority(StringRef s);
 
 InputSection *getFirstInputSection(const OutputSection *os);
-SmallVector<InputSection *, 0> getInputSections(const OutputSection &os);
+llvm::ArrayRef<InputSection *>
+getInputSections(const OutputSection &os,
+                 SmallVector<InputSection *, 0> &storage);
 
 // All output sections that are handled by the linker specially are
 // globally accessible. Writer initializes them, so don't use them

diff  --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp
index 7bfe29eda695..8ac6fc7cb831 100644
--- a/lld/ELF/Writer.cpp
+++ b/lld/ELF/Writer.cpp
@@ -1741,6 +1741,7 @@ static void fixSymbolsAfterShrinking() {
 // option is used.
 template <class ELFT> void Writer<ELFT>::optimizeBasicBlockJumps() {
   assert(config->optimizeBBJumps);
+  SmallVector<InputSection *, 0> storage;
 
   script->assignAddresses();
   // For every output section that has executable input sections, this
@@ -1752,7 +1753,7 @@ template <class ELFT> void Writer<ELFT>::optimizeBasicBlockJumps() {
   for (OutputSection *osec : outputSections) {
     if (!(osec->flags & SHF_EXECINSTR))
       continue;
-    SmallVector<InputSection *, 0> sections = getInputSections(*osec);
+    ArrayRef<InputSection *> sections = getInputSections(*osec, storage);
     size_t numDeleted = 0;
     // Delete all fall through jump instructions.  Also, check if two
     // consecutive jump instructions can be flipped so that a fall
@@ -1772,7 +1773,7 @@ template <class ELFT> void Writer<ELFT>::optimizeBasicBlockJumps() {
   fixSymbolsAfterShrinking();
 
   for (OutputSection *osec : outputSections)
-    for (InputSection *is : getInputSections(*osec))
+    for (InputSection *is : getInputSections(*osec, storage))
       is->trim();
 }
 
@@ -2165,9 +2166,10 @@ template <class ELFT> void Writer<ELFT>::checkExecuteOnly() {
   if (!config->executeOnly)
     return;
 
+  SmallVector<InputSection *, 0> storage;
   for (OutputSection *osec : outputSections)
     if (osec->flags & SHF_EXECINSTR)
-      for (InputSection *isec : getInputSections(*osec))
+      for (InputSection *isec : getInputSections(*osec, storage))
         if (!(isec->flags & SHF_EXECINSTR))
           error("cannot place " + toString(isec) + " into " +
                 toString(osec->name) +