[clang] [CIR] Unreacheable blocks should be target lowered (PR #224609)

[Mariya Podchishchaeva via cfe-commits]

https://github.com/Fznamznon created https://github.com/llvm/llvm-project/pull/224609

Similar to CXXABILowering and LowerToLLVM, target lowering should also transform unreacheable blocks to avoid legalization failures.

>From 1d801ff87af12b0306f6020c779fd5eaee883e68 Mon Sep 17 00:00:00 2001
From: Mariya Podchishchaeva <Mariya.Podchishchaeva at amd.com>
Date: Fri, 18 Sep 2026 06:41:46 -0500
Subject: [PATCH] [CIR] Unreacheable blocks should be target lowered

Similar to CXXABILowering and LowerToLLVM, target lowering
should also transform unreacheable blocks to avoid legalization
failures.
---
 .../CIR/Dialect/Transforms/TargetLowering.cpp |  7 +++-
 .../CodeGen/target-lowering-dead-block.cpp    | 34 +++++++++++++++++++
 2 files changed, 40 insertions(+), 1 deletion(-)
 create mode 100644 clang/test/CIR/CodeGen/target-lowering-dead-block.cpp

diff --git a/clang/lib/CIR/Dialect/Transforms/TargetLowering.cpp b/clang/lib/CIR/Dialect/Transforms/TargetLowering.cpp
index aa782aedfda1d..22ffeedc8b3af 100644
--- a/clang/lib/CIR/Dialect/Transforms/TargetLowering.cpp
+++ b/clang/lib/CIR/Dialect/Transforms/TargetLowering.cpp
@@ -20,6 +20,7 @@
 #include "clang/CIR/Dialect/IR/CIRDialect.h"
 #include "clang/CIR/Dialect/IR/CIRTypes.h"
 #include "clang/CIR/Dialect/Passes.h"
+#include "clang/CIR/Dialect/Transforms/CIRTransformUtils.h"
 
 using namespace mlir;
 using namespace cir;
@@ -320,7 +321,11 @@ void TargetLoweringPass::runOnOperation() {
   mlir::ConversionTarget target(*mod.getContext());
   populateTargetLoweringConversionTarget(target, typeConverter);
 
-  if (failed(mlir::applyPartialConversion(mod, target, std::move(patterns))))
+  llvm::SmallVector<mlir::Operation *> ops;
+  ops.push_back(mod);
+  cir::collectUnreachable(mod, ops);
+
+  if (failed(mlir::applyPartialConversion(ops, target, std::move(patterns))))
     signalPassFailure();
 }
 
diff --git a/clang/test/CIR/CodeGen/target-lowering-dead-block.cpp b/clang/test/CIR/CodeGen/target-lowering-dead-block.cpp
new file mode 100644
index 0000000000000..c738e5d1eade6
--- /dev/null
+++ b/clang/test/CIR/CodeGen/target-lowering-dead-block.cpp
@@ -0,0 +1,34 @@
+// RUN: %clang_cc1 -fcuda-is-device -triple amdgpu -fclangir -emit-cir -mmlir -mlir-print-ir-before=cir-target-lowering %s -o %t.cir 2> %t.pre.cir
+// RUN: FileCheck --check-prefix=CIR,CIR-PRE --input-file=%t.pre.cir %s
+// RUN: FileCheck --check-prefix=CIR,CIR-POST --input-file=%t.cir %s
+
+__attribute__((device)) int test(int input) {
+  int a = input;
+  if (!input) {
+    __builtin_trap();
+    return a;
+  } else {
+    return a;
+  }
+}
+
+// CIR-LABEL: cir.func {{.*}}@_Z4testi
+
+// CIR-PRE:       %[[RETVAL:.*]] = cir.alloca "__retval" {{.*}} : !cir.ptr<!s32i, lang_address_space(offload_private)>
+// CIR-POST:      %[[RETVAL:.*]] = cir.alloca "__retval" {{.*}} : !cir.ptr<!s32i, target_address_space(5)>
+
+// CIR-PRE:       %[[A:.*]] = cir.alloca "a" align(4) init : !cir.ptr<!s32i, lang_address_space(offload_private)>
+// CIR-POST:       %[[A:.*]] = cir.alloca "a" align(4) init : !cir.ptr<!s32i, target_address_space(5)>
+
+// CIR-POST-NOT:  builtin.unrealized_conversion_cast
+
+// CIR-PRE:       %[[ACAST:.*]] = cir.cast address_space %[[A]] : !cir.ptr<!s32i, lang_address_space(offload_private)> -> !cir.ptr<!s32i>
+// CIR-POST:      %[[ACAST:.*]] = cir.cast address_space %[[A]] : !cir.ptr<!s32i, target_address_space(5)> -> !cir.ptr<!s32i>
+
+// CIR:           cir.trap
+// CIR:           %[[LOAD:.*]] = cir.load align(4) %[[ACAST]] : !cir.ptr<!s32i>, !s32i
+// CIR-PRE-NEXT:  cir.store %[[LOAD]], %[[RETVAL]] : !s32i, !cir.ptr<!s32i, lang_address_space(offload_private)>
+// CIR-PRE-NEXT:  %[[RET:.*]] = cir.load %[[RETVAL]] : !cir.ptr<!s32i, lang_address_space(offload_private)>, !s32i
+// CIR-POST-NEXT: cir.store %[[LOAD]], %[[RETVAL]] : !s32i, !cir.ptr<!s32i, target_address_space(5)>
+// CIR-POST-NEXT: %[[RET:.*]] = cir.load %[[RETVAL]] : !cir.ptr<!s32i, target_address_space(5)>, !s32i
+// CIR-NEXT:      cir.return %[[RET]] : !s32i