[mlir] remove some GCC warning (#68409)

also remove `comparison of unsigned expression >= 0`

mlir/CMakeLists.txt

@@ -77,6 +77,15 @@ check_c_compiler_flag("-Werror=mismatched-tags" C_SUPPORTS_WERROR_MISMATCHED_TAG
 append_if(C_SUPPORTS_WERROR_MISMATCHED_TAGS "-Werror=mismatched-tags" CMAKE_C_FLAGS)
 append_if(C_SUPPORTS_WERROR_MISMATCHED_TAGS "-Werror=mismatched-tags" CMAKE_CXX_FLAGS)
 
+# Silence a false positive GCC -Wunused-but-set-parameter warning in constexpr
+# cases, by marking SelectedCase as used. See
+# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85827 for details. The issue is
+# fixed in GCC 10.
+if(CMAKE_CXX_COMPILER_ID MATCHES "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS "10.0")
+  check_cxx_compiler_flag("-Wno-unused-but-set-parameter" CXX_SUPPORTS_WNO_UNUSED_BUT_SET_PARAMETER)
+  append_if(CXX_SUPPORTS_WNO_UNUSED_BUT_SET_PARAMETER "-Wno-unused-but-set-parameter" CMAKE_CXX_FLAGS)
+endif()
+
 # Installing the headers and docs needs to depend on generating any public
 # tablegen'd targets.
 # mlir-generic-headers are dialect-independent.

mlir/lib/Dialect/Transform/IR/TransformOps.cpp

@@ -1996,7 +1996,7 @@ void transform::SplitHandleOp::getEffects(
 
 LogicalResult transform::SplitHandleOp::verify() {
   if (getOverflowResult().has_value() &&
-      !(*getOverflowResult() >= 0 && *getOverflowResult() < getNumResults()))
+      !(*getOverflowResult() < getNumResults()))
     return emitOpError("overflow_result is not a valid result index");
   return success();
 }