[llvm] [ThinLTO] Don't mark calloc function dead (PR #72673)

[via llvm-commits]

https://github.com/eleviant updated https://github.com/llvm/llvm-project/pull/72673

>From 410bd0c768f3a9c314b2d7971397dc686502cb14 Mon Sep 17 00:00:00 2001
From: Evgeny Leviant <eleviant at accesssoftek.com>
Date: Fri, 17 Nov 2023 15:32:24 +0300
Subject: [PATCH] [ThinLTO] Don't mark calloc function dead

Dead store elimination pass may fold malloc + memset calls into a
single call to calloc. If calloc is not preserved and is not being
called directly it can be marked dead during thin link and result
in link error.
---
 llvm/lib/Object/IRSymtab.cpp           |  4 +++
 llvm/test/ThinLTO/X86/Inputs/calloc.ll | 20 +++++++++++++++
 llvm/test/ThinLTO/X86/call-calloc.ll   | 35 ++++++++++++++++++++++++++
 3 files changed, 59 insertions(+)
 create mode 100644 llvm/test/ThinLTO/X86/Inputs/calloc.ll
 create mode 100644 llvm/test/ThinLTO/X86/call-calloc.ll

diff --git a/llvm/lib/Object/IRSymtab.cpp b/llvm/lib/Object/IRSymtab.cpp
index 18fc2e4d4a37b21..4232c7ada9075fa 100644
--- a/llvm/lib/Object/IRSymtab.cpp
+++ b/llvm/lib/Object/IRSymtab.cpp
@@ -54,6 +54,10 @@ static const char *PreservedSymbols[] = {
     // TODO: Are there similar such variables?
     "__ssp_canary_word",
     "__stack_chk_guard",
+    // The dead store elimination pass can fold malloc + memset calls into
+    // a single call to calloc. Prevent thin LTO from marking calloc a dead
+    // function otherwise we may face link errors.
+    "calloc",
 };
 
 namespace {
diff --git a/llvm/test/ThinLTO/X86/Inputs/calloc.ll b/llvm/test/ThinLTO/X86/Inputs/calloc.ll
new file mode 100644
index 000000000000000..1f7c0a432f82851
--- /dev/null
+++ b/llvm/test/ThinLTO/X86/Inputs/calloc.ll
@@ -0,0 +1,20 @@
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+ at _ZZ6mallocE3buf = internal global [2000 x i8] zeroinitializer, align 1
+
+define hidden ptr @malloc(i64 %a) {
+entry:
+  ret ptr @_ZZ6mallocE3buf
+}
+
+define hidden ptr @calloc(i64 noundef %num, i64 noundef %size) {
+entry:
+  %mul = mul i64 %size, %num
+  %call = tail call noalias ptr @malloc(i64 poison)
+  tail call void @llvm.memset.p0.i64(ptr nonnull align 1 @_ZZ6mallocE3buf, i8 0, i64 %mul, i1 false)
+  ret ptr @_ZZ6mallocE3buf
+}
+
+declare void @llvm.memset.p0.i64(ptr nocapture writeonly, i8, i64, i1 immarg)
+
diff --git a/llvm/test/ThinLTO/X86/call-calloc.ll b/llvm/test/ThinLTO/X86/call-calloc.ll
new file mode 100644
index 000000000000000..c087b3315403123
--- /dev/null
+++ b/llvm/test/ThinLTO/X86/call-calloc.ll
@@ -0,0 +1,35 @@
+; RUN: opt -module-summary %s -o %t1.bc
+; RUN: opt -module-summary %p/Inputs/calloc.ll -o %t2.bc
+; RUN: llvm-lto2 run -save-temps -o %t.out \
+; RUN:   %t1.bc -r=%t1.bc,_Z7DoStuffv,px -r=%t1.bc,_ZnwmRKSt9nothrow_t,px \
+; RUN:          -r=%t1.bc,_ZSt7nothrow -r=%t1.bc,malloc,l \
+; RUN:   %t2.bc -r=%t2.bc,malloc,pl -r=%t2.bc,calloc,pl
+; RUN: llvm-dis %t.out.2.5.precodegen.bc -o - | FileCheck %s
+
+; CHECK: define {{.*}} @calloc
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+%"struct.std::nothrow_t" = type { i8 }
+
+ at _ZSt7nothrow = external global %"struct.std::nothrow_t", align 1
+
+declare ptr @malloc(i64)
+
+define ptr @_ZnwmRKSt9nothrow_t(i64 %size, ptr %0) {
+entry:
+  %call = tail call noalias ptr @malloc(i64 %size)
+  ret ptr %call
+}
+
+define void @_Z7DoStuffv() {
+entry:
+  %call = tail call ptr @_ZnwmRKSt9nothrow_t(i64 400, ptr @_ZSt7nothrow)
+  %new.isnull = icmp ne ptr %call, null
+  tail call void @llvm.memset.p0.i64(ptr %call, i8 0, i64 400, i1 false)
+  ret void
+}
+
+declare void @llvm.memset.p0.i64(ptr nocapture writeonly, i8, i64, i1 immarg)
+