[Windows] Put init_seg(compiler/lib) in llvm.global_ctors

Currently we treat initializers with init_seg(compiler/lib) as similar
to any other init_seg, they simply have a global variable in the proper
section (".CRT$XCC" for compiler/".CRT$XCL" for lib) and are added to
llvm.used. However, this doesn't match with how LLVM sees normal (or
init_seg(user)) initializers via llvm.global_ctors. This
causes issues like incorrect init_seg(compiler) vs init_seg(user)
ordering due to GlobalOpt evaluating constructors, and the
ability to remove init_seg(compiler/lib) initializers at all.

Currently we use 'A' for priorities less than 200. Use 200 for
init_seg(compiler) (".CRT$XCC") and 400 for init_seg(lib) (".CRT$XCL"),
which do not append the priority to the section name. Priorities
between 200 and 400 use ".CRT$XCC${Priority}". This allows for
some wiggle room for people/future extensions that want to add
initializers between compiler and lib.

Fixes #56922

Reviewed By: rnk

Differential Revision: https://reviews.llvm.org/D131910

1 files changed, 16 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index 5859937..941e6a2 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -1889,11 +1889,24 @@ static MCSectionCOFF *getCOFFStaticStructorSection(MCContext &Ctx,
     // string that sorts between .CRT$XCA and .CRT$XCU. In the general case, we
     // make a name like ".CRT$XCT12345", since that runs before .CRT$XCU. Really
     // low priorities need to sort before 'L', since the CRT uses that
-    // internally, so we use ".CRT$XCA00001" for them.
+    // internally, so we use ".CRT$XCA00001" for them. We have a contract with
+    // the frontend that "init_seg(compiler)" corresponds to priority 200 and
+    // "init_seg(lib)" corresponds to priority 400, and those respectively use
+    // 'C' and 'L' without the priority suffix. Priorities between 200 and 400
+    // use 'C' with the priority as a suffix.
     SmallString<24> Name;
+    char LastLetter = 'T';
+    bool AddPrioritySuffix = Priority != 200 && Priority != 400;
+    if (Priority < 200)
+      LastLetter = 'A';
+    else if (Priority < 400)
+      LastLetter = 'C';
+    else if (Priority == 400)
+      LastLetter = 'L';
     raw_svector_ostream OS(Name);
-    OS << ".CRT$X" << (IsCtor ? "C" : "T") <<
-        (Priority < 200 ? 'A' : 'T') << format("%05u", Priority);
+    OS << ".CRT$X" << (IsCtor ? "C" : "T") << LastLetter;
+    if (AddPrioritySuffix)
+      OS << format("%05u", Priority);
     MCSectionCOFF *Sec = Ctx.getCOFFSection(
         Name, COFF::IMAGE_SCN_CNT_INITIALIZED_DATA | COFF::IMAGE_SCN_MEM_READ,
         SectionKind::getReadOnly());