[BugFix][LLVM] Fix insertDeclare API mismatch for ROCm-bundled LLVM 20

ROCm ships its own LLVM 20 build that still uses the pre-LLVM-20
`Instruction*` overload of `DIBuilder::insertDeclare`, while upstream
LLVM 20 switched to `BasicBlock::iterator`. The previous version-number
guard `#if TVM_LLVM_VERSION >= 200` broke ROCm users on LLVM 20.

Replace the version guard with a CMake `check_cxx_source_compiles`
feature probe (`TVM_LLVM_INSERTDECLARE_USES_ITERATOR`) that compiles a
small test program to detect which overload is actually available.
Use `cmake_push_check_state`/`cmake_pop_check_state` to avoid leaking
CMake check variables. Three call sites in `codegen_llvm.cc` are
updated to use the new macro.

Fixes #18709

Author: swjng

cmake/utils/FindLLVM.cmake

@@ -237,4 +237,31 @@ macro(find_llvm use_llvm)
     message(FATAL_ERROR "TVM requires LLVM 15.0 or higher.")
   endif()
   message(STATUS "Found TVM_LLVM_HAS_AARCH64_TARGET=" ${TVM_LLVM_HAS_AARCH64_TARGET})
+
+  # Detect whether DIBuilder::insertDeclare accepts BasicBlock::iterator
+  # as the insertion point (upstream LLVM 20+) vs Instruction* (pre-LLVM 20
+  # and ROCm-bundled LLVM 20, which reports version 200 but lacks this overload).
+  if (${TVM_LLVM_VERSION} GREATER_EQUAL 200)
+    include(CheckCXXSourceCompiles)
+    include(CMakePushCheckState)
+    cmake_push_check_state(RESET)
+    set(CMAKE_REQUIRED_INCLUDES ${LLVM_INCLUDE_DIRS})
+    set(CMAKE_REQUIRED_FLAGS "-std=c++17 -fno-rtti")
+    check_cxx_source_compiles("
+      #include <llvm/IR/DIBuilder.h>
+      #include <llvm/IR/Instructions.h>
+      void f(llvm::DIBuilder* b, llvm::Value* v, llvm::DILocalVariable* var,
+             llvm::DIExpression* e, const llvm::DILocation* dl,
+             llvm::Instruction* i) {
+        b->insertDeclare(v, var, e, dl, llvm::BasicBlock::iterator(i));
+      }
+    " TVM_LLVM_INSERTDECLARE_USES_ITERATOR)
+    cmake_pop_check_state()
+    if(TVM_LLVM_INSERTDECLARE_USES_ITERATOR)
+      add_definitions(-DTVM_LLVM_INSERTDECLARE_USES_ITERATOR=1)
+      message(STATUS "LLVM DIBuilder::insertDeclare uses BasicBlock::iterator")
+    else()
+      message(STATUS "LLVM DIBuilder::insertDeclare uses Instruction* (ROCm or older LLVM 20)")
+    endif()
+  endif()
 endmacro(find_llvm)

src/target/llvm/codegen_llvm.cc

@@ -2147,7 +2147,7 @@ void CodeGenLLVM::AddDebugInformation(llvm::Function* f_llvm,
 
     auto* store = builder.CreateStore(iter_param, paramAlloca);
     auto* di_loc = llvm::DILocation::get(*ctx, 0, 0, di_subprogram_);
-#if TVM_LLVM_VERSION >= 200
+#if TVM_LLVM_INSERTDECLARE_USES_ITERATOR
     dbg_info_->di_builder_->insertDeclare(
         paramAlloca, param, dbg_info_->di_builder_->createExpression(), llvm::DebugLoc(di_loc),
         llvm::BasicBlock::iterator(store));
@@ -2193,9 +2193,10 @@ void CodeGenLLVM::AddDebugInformation(llvm::Value* llvm_value, const Var& tir_va
   // the SSA value directly rather than a memory location.
   if (!llvm_value->getType()->isPointerTy()) {
     if (insert_before) {
-      // LLVM 20+ changed insertDbgValueIntrinsic to take BasicBlock::iterator
-      // instead of Instruction* for the insertion point.
-#if TVM_LLVM_VERSION >= 200
+      // Upstream LLVM 20+ changed insertDbgValueIntrinsic to take
+      // BasicBlock::iterator; ROCm-bundled LLVM 20 retains Instruction*.
+      // TVM_LLVM_INSERTDECLARE_USES_ITERATOR is set by CMake feature detection.
+#if TVM_LLVM_INSERTDECLARE_USES_ITERATOR
       dbg_info_->di_builder_->insertDbgValueIntrinsic(
           llvm_value, local_var, dbg_info_->di_builder_->createExpression(), llvm::DebugLoc(di_loc),
           llvm::BasicBlock::iterator(insert_before));
@@ -2213,7 +2214,7 @@ void CodeGenLLVM::AddDebugInformation(llvm::Value* llvm_value, const Var& tir_va
   }
 
   if (insert_before) {
-#if TVM_LLVM_VERSION >= 200
+#if TVM_LLVM_INSERTDECLARE_USES_ITERATOR
     dbg_info_->di_builder_->insertDeclare(
         llvm_value, local_var, dbg_info_->di_builder_->createExpression(), llvm::DebugLoc(di_loc),
         llvm::BasicBlock::iterator(insert_before));