[llvm-branch-commits] [llvm] [llvm][IR] Treat memcmp and bcmp as libcalls (PR #135706)

[via llvm-branch-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-lto

Author: Paul Kirth (ilovepi)

<details>
<summary>Changes</summary>

Since the backend may emit calls to these functions, they should be
treated like other libcalls. If we don't, then it is possible to
have their definitions removed during LTO because they are dead, only to
have a later transform introduce calls to them.

See https://discourse.llvm.org/t/rfc-addressing-deficiencies-in-llvm-s-lto-implementation/84999
for more information.

---
Full diff: https://github.com/llvm/llvm-project/pull/135706.diff


2 Files Affected:

- (modified) llvm/include/llvm/IR/RuntimeLibcalls.def (+2) 
- (modified) llvm/test/LTO/Resolution/RISCV/bcmp-libcall.ll (+1-2) 


``````````diff
diff --git a/llvm/include/llvm/IR/RuntimeLibcalls.def b/llvm/include/llvm/IR/RuntimeLibcalls.def
index 2545aebc73391..2c72bc8c012cc 100644
--- a/llvm/include/llvm/IR/RuntimeLibcalls.def
+++ b/llvm/include/llvm/IR/RuntimeLibcalls.def
@@ -513,6 +513,8 @@ HANDLE_LIBCALL(UO_PPCF128, "__gcc_qunord")
 HANDLE_LIBCALL(MEMCPY, "memcpy")
 HANDLE_LIBCALL(MEMMOVE, "memmove")
 HANDLE_LIBCALL(MEMSET, "memset")
+HANDLE_LIBCALL(MEMCMP, "memcmp")
+HANDLE_LIBCALL(BCMP, "bcmp")
 // DSEPass can emit calloc if it finds a pair of malloc/memset
 HANDLE_LIBCALL(CALLOC, "calloc")
 HANDLE_LIBCALL(BZERO, nullptr)
diff --git a/llvm/test/LTO/Resolution/RISCV/bcmp-libcall.ll b/llvm/test/LTO/Resolution/RISCV/bcmp-libcall.ll
index 4c6bebf69a074..80421cd9350c8 100644
--- a/llvm/test/LTO/Resolution/RISCV/bcmp-libcall.ll
+++ b/llvm/test/LTO/Resolution/RISCV/bcmp-libcall.ll
@@ -29,8 +29,7 @@ define i1 @foo(ptr %0, [2 x i32] %1) {
 declare i32 @memcmp(ptr, ptr, i32)
 
 ;; Ensure bcmp is removed from module. Follow up patches can address this.
-; INTERNALIZE-NOT: declare{{.*}}i32 @bcmp
-; INTERNALIZE-NOT: define{{.*}}i32 @bcmp
+; INTERNALIZE: define{{.*}}i32 @bcmp
 define i32 @bcmp(ptr %0, ptr %1, i32 %2) {
   ret i32 0
 }

``````````

</details>


https://github.com/llvm/llvm-project/pull/135706