[llvm-branch-commits] [lld] ELF: CFI jump table relaxation. (PR #147424)

[Vitaly Buka via llvm-branch-commits]

================
@@ -312,6 +313,193 @@ bool X86_64::deleteFallThruJmpInsn(InputSection &is,
   return true;
 }
 
+void X86_64::relaxCFIJumpTables() const {
+  // Relax CFI jump tables.
+  // - Split jump table into pieces and place target functions inside the jump
+  //   table if small enough.
+  // - Move jump table before last called function and delete last branch
+  //   instruction.
+  DenseMap<InputSection *, std::vector<InputSection *>> sectionReplacements;
+  SmallVector<InputSection *, 0> storage;
+  for (OutputSection *osec : ctx.outputSections) {
+    if (!(osec->flags & SHF_EXECINSTR))
+      continue;
+    for (InputSection *sec : getInputSections(*osec, storage)) {
+      if (sec->type != SHT_LLVM_CFI_JUMP_TABLE || sec->entsize == 0 ||
+          sec->size % sec->entsize != 0)
+        continue;
+
+      // We're going to replace the jump table with this list of sections. This
+      // list will be made up of slices of the original section and function
+      // bodies that were moved into the jump table.
+      std::vector<InputSection *> replacements;
+
+      // Add the slice [begin, end) of the original section to the replacement
+      // list. [rbegin, rend) is the slice of the relocation list that covers
+      // [begin, end).
----------------
vitalybuka wrote:

addSectionSlice can be moved closer to the user

https://github.com/llvm/llvm-project/pull/147424