[llvm] [mlir] [MLIR][CMake] Suppress -Wpass-failed warning (PR #160472)

[Nikita Popov via llvm-commits]

https://github.com/nikic updated https://github.com/llvm/llvm-project/pull/160472

>From 1e2a48787a3d33c6253fe414901ae2903b51e229 Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov at redhat.com>
Date: Wed, 24 Sep 2025 10:54:00 +0200
Subject: [PATCH 1/2] [MLIR][CMake] Suppress -Wpass-failed warning

libstdc++15 makes use of an unroll pragma inside std::find_if(). This
produces a warning if clang fails to unroll the loop. As this pragma is
outside of our control, suppress the warning.
---
 mlir/CMakeLists.txt | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mlir/CMakeLists.txt b/mlir/CMakeLists.txt
index 1a211f5495764..da340c4e36784 100644
--- a/mlir/CMakeLists.txt
+++ b/mlir/CMakeLists.txt
@@ -110,6 +110,12 @@ if(CMAKE_CXX_COMPILER_ID MATCHES "GNU")
   endif()
 endif()
 
+# libstdc++15 makes use of an unroll pragma inside std::find_if(). This
+# produces a warning if clang fails to unroll the loop. As this pragma is
+# outside of our control, suppress the warning.
+check_cxx_compiler_flag("-Wno-pass-failed" CXX_SUPPORTS_WNO_PASS_FAILED)
+append_if(CXX_SUPPORTS_WNO_PASS_FAILED "-Wno-pass-failed" CMAKE_CXX_FLAGS)
+
 # Installing the headers and docs needs to depend on generating any public
 # tablegen'd targets.
 # mlir-generic-headers are dialect-independent.

>From f203d441910b88276f647f8a6ba93e827d5dcc26 Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov at redhat.com>
Date: Mon, 29 Sep 2025 12:38:11 +0200
Subject: [PATCH 2/2] Move to llvm, add FIXME to possibly remove it again

---
 llvm/cmake/modules/HandleLLVMOptions.cmake | 7 +++++++
 mlir/CMakeLists.txt                        | 6 ------
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/llvm/cmake/modules/HandleLLVMOptions.cmake b/llvm/cmake/modules/HandleLLVMOptions.cmake
index 8eca29f8a03f5..6d61e0919400e 100644
--- a/llvm/cmake/modules/HandleLLVMOptions.cmake
+++ b/llvm/cmake/modules/HandleLLVMOptions.cmake
@@ -962,6 +962,13 @@ if (LLVM_ENABLE_WARNINGS AND (LLVM_COMPILER_IS_GCC_COMPATIBLE OR CLANG_CL))
 
   # Enable -Wctad-maybe-unsupported to catch unintended use of CTAD.
   add_flag_if_supported("-Wctad-maybe-unsupported" CTAD_MAYBE_UNSPPORTED_FLAG)
+
+  # Disable -Wno-pass-failed flag, which reports failure to perform
+  # optimizations suggested by pragmas. This warning is not relevant for LLVM
+  # projects and may be injected by pragmas in libstdc++.
+  # FIXME: Reconsider this choice if warnings from STL headers can be reliably
+  # avoided (https://github.com/llvm/llvm-project/issues/157666).
+  add_flag_if_supported("-Wno-pass-failed" NO_PASS_FAILED_FLAG)
 endif (LLVM_ENABLE_WARNINGS AND (LLVM_COMPILER_IS_GCC_COMPATIBLE OR CLANG_CL))
 
 if (LLVM_COMPILER_IS_GCC_COMPATIBLE AND NOT LLVM_ENABLE_WARNINGS)
diff --git a/mlir/CMakeLists.txt b/mlir/CMakeLists.txt
index da340c4e36784..1a211f5495764 100644
--- a/mlir/CMakeLists.txt
+++ b/mlir/CMakeLists.txt
@@ -110,12 +110,6 @@ if(CMAKE_CXX_COMPILER_ID MATCHES "GNU")
   endif()
 endif()
 
-# libstdc++15 makes use of an unroll pragma inside std::find_if(). This
-# produces a warning if clang fails to unroll the loop. As this pragma is
-# outside of our control, suppress the warning.
-check_cxx_compiler_flag("-Wno-pass-failed" CXX_SUPPORTS_WNO_PASS_FAILED)
-append_if(CXX_SUPPORTS_WNO_PASS_FAILED "-Wno-pass-failed" CMAKE_CXX_FLAGS)
-
 # Installing the headers and docs needs to depend on generating any public
 # tablegen'd targets.
 # mlir-generic-headers are dialect-independent.