[IR][ModRef] Introduce `errno` memory location

Model C/C++ `errno` macro by adding a corresponding `errno`
memory location kind to the IR. Preliminary work to separate
`errno` writes from other memory accesses, to the benefit of
alias analyses and optimization correctness.

Previous discussion: https://discourse.llvm.org/t/rfc-modelling-errno-memory-effects/82972.

1 files changed, 3 insertions, 0 deletions

diff --git a/llvm/lib/IR/Attributes.cpp b/llvm/lib/IR/Attributes.cpp
index ef0591e..8da1dfe 100644
--- a/llvm/lib/IR/Attributes.cpp
+++ b/llvm/lib/IR/Attributes.cpp
@@ -647,6 +647,9 @@ std::string Attribute::getAsString(bool InAttrGrp) const {
       case IRMemLocation::InaccessibleMem:
         OS << "inaccessiblemem: ";
         break;
+      case IRMemLocation::ErrnoMem:
+        OS << "errnomem: ";
+        break;
       case IRMemLocation::Other:
         llvm_unreachable("This is represented as the default access kind");
       }