commit f5e13efc48e1821d5bb85e254337263e50031de0
author Fangrui Song <maskray@google.com> Mon Sep 02 10:33:58 2019 +0000
committer Fangrui Song <maskray@google.com> Mon Sep 02 10:33:58 2019 +0000
tree 011613be5bf69a86bec0fa4ab89babe1df9f2eb4
parent 94eb853ee2cda2c7fd2531130862e4ad7b3b650d

[ELF] Do not ICF two sections with different output sections (by SECTIONS commands)

Fixes PR39418. Complements D47241 (the non-linker-script case).

processSectionCommands() assigns input sections to output sections.
ICF is called before it, so .text.foo and .text.bar may be folded even if
their output sections are made different by SECTIONS commands.

```
markLive<ELFT>()
doIcf<ELFT>()                      // During ICF, we don't know the output sections
writeResult()
  combineEhSections<ELFT>()
  script->processSectionCommands() // InputSection -> OutputSection assignment
```

This patch splits processSectionCommands() into processSectionCommands() and
processSymbolAssignments(), and moves processSectionCommands() before ICF:

```
markLive<ELFT>()
combineEhSections<ELFT>()
script->processSectionCommands()
doIcf<ELFT>()                      // should remove folded input sections
writeResult()
  script->processSymbolAssignments()
```

An alternative approach is to unfold a section `sec` in
processSectionCommands() when we find `sec` and `sec->repl` belong to
different output sections. I feel this patch is superior because this
can fold more sections and the decouple of
SectionCommand/SymbolAssignment gives flexibility:

* An ExprValue can't be evaluated before its section is assigned to an
  output section -> we can delete getOutputSectionVA and simplify
  another place where we had to check if the output section is null.
  Moreover, a case in linkerscript/early-assign-symbol.s can be handled
  now.
* processSectionCommands/processSymbolAssignments can be freely moved
  around.

Reviewed By: ruiu

Differential Revision: https://reviews.llvm.org/D66717

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@370635 91177308-0d34-0410-b5e6-96231b3b80d8