[llvm] [cmake] Extend zstd.dll finding logic from MSVC to WIN32 in general (PR #121437)

[Michał Górny via llvm-commits]

https://github.com/mgorny updated https://github.com/llvm/llvm-project/pull/121437

>From 003686fd6ae6c3ef026bff3e601010bdd3ad5f36 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Micha=C5=82=20G=C3=B3rny?= <mgorny at gentoo.org>
Date: Wed, 1 Jan 2025 16:25:26 +0100
Subject: [PATCH 1/2] [cmake] Extend zstd.dll finding logic from MSVC to WIN32
 in general

Extend the special logic for finding `zstd.dll` in `Findzstd` to apply
to all Windows configurations rather than just MSVC.  From what
I understand, this naming scheme is specific to Windows in general,
rather than "Windows with MSVC", and `.lib` files are always used to
link to shared libraries.  I could reproduce the original problem when
using Clang with Conda-installed LLVM, and extending the logic to
`WIN32` seems to fix it for me.

That said, I'm not an expert on Windows and I have only done very
limited testing, so I'd appreciate if someone could double check that
I'm not breaking some workflow.

Fixes #121345
---
 llvm/cmake/modules/Findzstd.cmake | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/llvm/cmake/modules/Findzstd.cmake b/llvm/cmake/modules/Findzstd.cmake
index 86b6d48b6ec6b6..6726e9ea940b92 100644
--- a/llvm/cmake/modules/Findzstd.cmake
+++ b/llvm/cmake/modules/Findzstd.cmake
@@ -10,7 +10,7 @@
 # zstd::libzstd_shared
 # zstd::libzstd_static
 
-if(MSVC)
+if(WIN32)
   set(zstd_STATIC_LIBRARY_SUFFIX "_static\\${CMAKE_STATIC_LIBRARY_SUFFIX}$")
 else()
   set(zstd_STATIC_LIBRARY_SUFFIX "\\${CMAKE_STATIC_LIBRARY_SUFFIX}$")
@@ -33,7 +33,7 @@ if(zstd_FOUND)
     set(zstd_STATIC_LIBRARY "${zstd_LIBRARY}")
   elseif (NOT TARGET zstd::libzstd_shared)
     add_library(zstd::libzstd_shared SHARED IMPORTED)
-    if(MSVC)
+    if(WIN32)
       include(GNUInstallDirs) # For CMAKE_INSTALL_LIBDIR and friends.
       # IMPORTED_LOCATION is the path to the DLL and IMPORTED_IMPLIB is the "library".
       get_filename_component(zstd_DIRNAME "${zstd_LIBRARY}" DIRECTORY)

>From 0e5ba65dad894d9ea0b3dfb8ded9d44551ded13a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Micha=C5=82=20G=C3=B3rny?= <mgorny at gentoo.org>
Date: Thu, 2 Jan 2025 11:25:58 +0100
Subject: [PATCH 2/2] [cmake] Use CMAKE_CXX_SIMULATE_ID to distinguish MSVC ABI
 in Findzstd

Instead of unconditionally assuming MSVC-alike behavior for WIN32 that
could negatively impact MSVC, use `CMAKE_CXX_SIMULATE_ID` to detect
Clang using MSVC ABI.  Note that this variable is unset for MSVC itself,
so use it alternatively to MSVC.  Thanks to @isuruf for the suggestion
(https://github.com/conda-forge/llvmdev-feedstock/issues/306#issuecomment-2567306830).
---
 llvm/cmake/modules/Findzstd.cmake | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/llvm/cmake/modules/Findzstd.cmake b/llvm/cmake/modules/Findzstd.cmake
index 6726e9ea940b92..f6ca5d1ebe546b 100644
--- a/llvm/cmake/modules/Findzstd.cmake
+++ b/llvm/cmake/modules/Findzstd.cmake
@@ -10,7 +10,7 @@
 # zstd::libzstd_shared
 # zstd::libzstd_static
 
-if(WIN32)
+if(MSVC OR "${CMAKE_CXX_SIMULATE_ID}" STREQUAL "MSVC")
   set(zstd_STATIC_LIBRARY_SUFFIX "_static\\${CMAKE_STATIC_LIBRARY_SUFFIX}$")
 else()
   set(zstd_STATIC_LIBRARY_SUFFIX "\\${CMAKE_STATIC_LIBRARY_SUFFIX}$")
@@ -33,7 +33,7 @@ if(zstd_FOUND)
     set(zstd_STATIC_LIBRARY "${zstd_LIBRARY}")
   elseif (NOT TARGET zstd::libzstd_shared)
     add_library(zstd::libzstd_shared SHARED IMPORTED)
-    if(WIN32)
+    if(MSVC OR "${CMAKE_CXX_SIMULATE_ID}" STREQUAL "MSVC")
       include(GNUInstallDirs) # For CMAKE_INSTALL_LIBDIR and friends.
       # IMPORTED_LOCATION is the path to the DLL and IMPORTED_IMPLIB is the "library".
       get_filename_component(zstd_DIRNAME "${zstd_LIBRARY}" DIRECTORY)