[IR] make -stack-alignment= into a module attr

Similar to D102742, specifying the stack alignment via CodegenOpts means
that this flag gets dropped during LTO, unless the command line is
re-specified as a plugin opt. Instead, encode this information as a
module level attribute so that we don't have to expose this llvm
internal flag when linking the Linux kernel with LTO.

Looks like external dependencies might need a fix:
* https://github.com/llvm-hs/llvm-hs/issues/345
* https://github.com/halide/Halide/issues/6079

Link: https://github.com/ClangBuiltLinux/linux/issues/1377

Reviewed By: tejohnson

Differential Revision: https://reviews.llvm.org/D103048

1 files changed, 11 insertions, 0 deletions

diff --git a/llvm/lib/IR/Module.cpp b/llvm/lib/IR/Module.cpp
index eae4e69..9b95550 100644
--- a/llvm/lib/IR/Module.cpp
+++ b/llvm/lib/IR/Module.cpp
@@ -721,6 +721,17 @@ void Module::setStackProtectorGuardOffset(int Offset) {
   addModuleFlag(ModFlagBehavior::Error, "stack-protector-guard-offset", Offset);
 }
 
+unsigned Module::getOverrideStackAlignment() const {
+  Metadata *MD = getModuleFlag("override-stack-alignment");
+  if (auto *CI = mdconst::dyn_extract_or_null<ConstantInt>(MD))
+    return CI->getZExtValue();
+  return 0;
+}
+
+void Module::setOverrideStackAlignment(unsigned Align) {
+  addModuleFlag(ModFlagBehavior::Error, "override-stack-alignment", Align);
+}
+
 void Module::setSDKVersion(const VersionTuple &V) {
   SmallVector<unsigned, 3> Entries;
   Entries.push_back(V.getMajor());