[llvm] [BOLT] Clean up jump table handling in non-reloc mode. NFCI (PR #119614)

[Maksim Panchenko via llvm-commits]

https://github.com/maksfb created https://github.com/llvm/llvm-project/pull/119614

This change affects non-relocation mode only. Prior to having CheckLargeFunctions pass, we could have emitted code for functions that was discarded at the end due to size limitations. Since we didn't know at the time of emission if the code would be discarded or not, we had to emit jump tables in separate sections and handle them separately. However, now we always run CheckLargeFunctions and make sure all emitted code is used. Thus, we can get rid of the special jump table handling.

>From 3a8da1d835595f8309aad81d554b888da4370f5f Mon Sep 17 00:00:00 2001
From: Maksim Panchenko <maks at fb.com>
Date: Thu, 16 Sep 2021 10:16:44 -0700
Subject: [PATCH] [BOLT] Clean up jump table handling for non-reloc. NFCI

This change affects non-relocation mode only. Prior to having
CheckLargeFunctions pass, we could have emitted code for functions that
was discarded at the end due to size limitations. Since we didn't know
at the time of emission if the code would be discarded or not, we had to
emit jump tables in separate sections and handle them separately.
However, now we always run CheckLargeFunctions and make sure all emitted
code is used. Thus, we can get rid of the special jump table handling.
---
 bolt/lib/Core/BinaryEmitter.cpp      | 26 +++++--------------
 bolt/lib/Rewrite/RewriteInstance.cpp | 37 ++--------------------------
 2 files changed, 8 insertions(+), 55 deletions(-)

diff --git a/bolt/lib/Core/BinaryEmitter.cpp b/bolt/lib/Core/BinaryEmitter.cpp
index f34a94c5779213..1744c1e5717224 100644
--- a/bolt/lib/Core/BinaryEmitter.cpp
+++ b/bolt/lib/Core/BinaryEmitter.cpp
@@ -730,30 +730,16 @@ void BinaryEmitter::emitJumpTables(const BinaryFunction &BF) {
       continue;
     if (opts::PrintJumpTables)
       JT.print(BC.outs());
-    if (opts::JumpTables == JTS_BASIC && BC.HasRelocations) {
+    if (opts::JumpTables == JTS_BASIC) {
       JT.updateOriginal();
     } else {
       MCSection *HotSection, *ColdSection;
-      if (opts::JumpTables == JTS_BASIC) {
-        // In non-relocation mode we have to emit jump tables in local sections.
-        // This way we only overwrite them when the corresponding function is
-        // overwritten.
-        std::string Name = ".local." + JT.Labels[0]->getName().str();
-        std::replace(Name.begin(), Name.end(), '/', '.');
-        BinarySection &Section =
-            BC.registerOrUpdateSection(Name, ELF::SHT_PROGBITS, ELF::SHF_ALLOC);
-        Section.setAnonymous(true);
-        JT.setOutputSection(Section);
-        HotSection = BC.getDataSection(Name);
-        ColdSection = HotSection;
+      if (BF.isSimple()) {
+        HotSection = ReadOnlySection;
+        ColdSection = ReadOnlyColdSection;
       } else {
-        if (BF.isSimple()) {
-          HotSection = ReadOnlySection;
-          ColdSection = ReadOnlyColdSection;
-        } else {
-          HotSection = BF.hasProfile() ? ReadOnlySection : ReadOnlyColdSection;
-          ColdSection = HotSection;
-        }
+        HotSection = BF.hasProfile() ? ReadOnlySection : ReadOnlyColdSection;
+        ColdSection = HotSection;
       }
       emitJumpTable(JT, HotSection, ColdSection);
     }
diff --git a/bolt/lib/Rewrite/RewriteInstance.cpp b/bolt/lib/Rewrite/RewriteInstance.cpp
index 76e1f0156f828d..27a2636438cdad 100644
--- a/bolt/lib/Rewrite/RewriteInstance.cpp
+++ b/bolt/lib/Rewrite/RewriteInstance.cpp
@@ -78,7 +78,6 @@ namespace opts {
 extern cl::list<std::string> HotTextMoveSections;
 extern cl::opt<bool> Hugify;
 extern cl::opt<bool> Instrument;
-extern cl::opt<JumpTableSupportLevel> JumpTables;
 extern cl::opt<bool> KeepNops;
 extern cl::opt<bool> Lite;
 extern cl::list<std::string> ReorderData;
@@ -3841,20 +3840,6 @@ void RewriteInstance::mapCodeSections(BOLTLinker::SectionMapper MapSection) {
     assert(Function.getImageSize() <= Function.getMaxSize() &&
            "Unexpected large function");
 
-    // Map jump tables if updating in-place.
-    if (opts::JumpTables == JTS_BASIC) {
-      for (auto &JTI : Function.JumpTables) {
-        JumpTable *JT = JTI.second;
-        BinarySection &Section = JT->getOutputSection();
-        Section.setOutputAddress(JT->getAddress());
-        Section.setOutputFileOffset(getFileOffsetForAddress(JT->getAddress()));
-        LLVM_DEBUG(dbgs() << "BOLT-DEBUG: mapping JT " << Section.getName()
-                          << " to 0x" << Twine::utohexstr(JT->getAddress())
-                          << '\n');
-        MapSection(Section, JT->getAddress());
-      }
-    }
-
     if (!Function.isSplit())
       continue;
 
@@ -5637,26 +5622,8 @@ void RewriteInstance::rewriteFile() {
     if (Function->getImageAddress() == 0 || Function->getImageSize() == 0)
       continue;
 
-    if (Function->getImageSize() > Function->getMaxSize()) {
-      assert(!BC->isX86() && "Unexpected large function.");
-      if (opts::Verbosity >= 1)
-        BC->errs() << "BOLT-WARNING: new function size (0x"
-                   << Twine::utohexstr(Function->getImageSize())
-                   << ") is larger than maximum allowed size (0x"
-                   << Twine::utohexstr(Function->getMaxSize())
-                   << ") for function " << *Function << '\n';
-
-      // Remove jump table sections that this function owns in non-reloc mode
-      // because we don't want to write them anymore.
-      if (!BC->HasRelocations && opts::JumpTables == JTS_BASIC) {
-        for (auto &JTI : Function->JumpTables) {
-          JumpTable *JT = JTI.second;
-          BinarySection &Section = JT->getOutputSection();
-          BC->deregisterSection(Section);
-        }
-      }
-      continue;
-    }
+    assert(Function.getImageSize() <= Function.getMaxSize() &&
+           "Unexpected large function");
 
     const auto HasAddress = [](const FunctionFragment &FF) {
       return FF.empty() ||