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

[Paul Kirth via llvm-branch-commits]

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

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.

>From af02216b9358166b635335491934ff44cdcc89a5 Mon Sep 17 00:00:00 2001
From: Paul Kirth <paulkirth at google.com>
Date: Mon, 14 Apr 2025 08:25:15 -0700
Subject: [PATCH] [llvm][IR] Treat memcmp and bcmp as libcalls

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.
---
 llvm/include/llvm/IR/RuntimeLibcalls.def       | 2 ++
 llvm/test/LTO/Resolution/RISCV/bcmp-libcall.ll | 3 +--
 2 files changed, 3 insertions(+), 2 deletions(-)

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
 }