[lld] [lld-macho] Fix ICF differentiation of safe_thunks relocs (PR #111811)

[via llvm-commits]

https://github.com/alx32 updated https://github.com/llvm/llvm-project/pull/111811

>From 85b148bb43a2e4aefeb777b3e14e473dd587b16b Mon Sep 17 00:00:00 2001
From: Alex B <alexborcan at meta.com>
Date: Thu, 10 Oct 2024 03:35:22 -0700
Subject: [PATCH] <Replace this line with a title. Use 1 line only, 67 chars or
 less>

Summary:

Test Plan:

Reviewers:

Subscribers:

Tasks:

Tags:
---
 lld/MachO/ICF.cpp                 | 11 +++++++
 lld/test/MachO/icf-safe-thunks.ll | 49 +++++++++++++++++++++++++++++++
 2 files changed, 60 insertions(+)

diff --git a/lld/MachO/ICF.cpp b/lld/MachO/ICF.cpp
index 2ff962b06e3679..aedaecfdeb2c01 100644
--- a/lld/MachO/ICF.cpp
+++ b/lld/MachO/ICF.cpp
@@ -147,6 +147,17 @@ bool ICF::equalsConstant(const ConcatInputSection *ia,
       isecB = rb.referent.get<InputSection *>();
     }
 
+    // Typically, we should not encounter sections marked with `keepUnique` at
+    // this point as they would have resulted in different hashes and therefore
+    // no need for a full comparison.
+    // However, in `safe_thunks` mode, it's possible for two different
+    // relocations to reference identical `keepUnique` functions that will be
+    // distinguished later via thunks - so we need to handle this case
+    // explicitly.
+    if ((isecA != isecB) && ((isecA->keepUnique && isCodeSection(isecA)) ||
+                             (isecB->keepUnique && isCodeSection(isecB))))
+      return false;
+
     if (isecA->parent != isecB->parent)
       return false;
     // Sections with identical parents should be of the same kind.
diff --git a/lld/test/MachO/icf-safe-thunks.ll b/lld/test/MachO/icf-safe-thunks.ll
index 238e90f952e160..95e00a5b98385b 100644
--- a/lld/test/MachO/icf-safe-thunks.ll
+++ b/lld/test/MachO/icf-safe-thunks.ll
@@ -22,6 +22,13 @@
 ; CHECK-ARM64-NEXT:   _func_3identical_v3_canmerge:
 ; CHECK-ARM64-NEXT:        mov {{.*}}, #0x21
 ;
+; CHECK-ARM64:        _func_call_thunked_1_nomerge:
+; CHECK-ARM64-NEXT:        stp	x29
+;
+; CHECK-ARM64:        _func_call_thunked_2_nomerge:
+; CHECK-ARM64-NEXT:   _func_call_thunked_2_merge:
+; CHECK-ARM64-NEXT:        stp	x29
+;
 ; CHECK-ARM64:        _call_all_funcs:
 ; CHECK-ARM64-NEXT:        stp  x29
 ;
@@ -43,6 +50,9 @@
 ; CHECK-ARM64-MAP-NEXT: 0x00000010 [  2] _func_3identical_v1_canmerge
 ; CHECK-ARM64-MAP-NEXT: 0x00000000 [  2] _func_3identical_v2_canmerge
 ; CHECK-ARM64-MAP-NEXT: 0x00000000 [  2] _func_3identical_v3_canmerge
+; CHECK-ARM64-MAP-NEXT: 0x00000020 [  2] _func_call_thunked_1_nomerge
+; CHECK-ARM64-MAP-NEXT: 0x00000020 [  2] _func_call_thunked_2_nomerge
+; CHECK-ARM64-MAP-NEXT: 0x00000000 [  2] _func_call_thunked_2_merge
 ; CHECK-ARM64-MAP-NEXT: 0x00000034 [  2] _call_all_funcs
 ; CHECK-ARM64-MAP-NEXT: 0x00000050 [  2] _take_func_addr
 ; CHECK-ARM64-MAP-NEXT: 0x00000004 [  2] _func_2identical_v2
@@ -125,6 +135,30 @@ entry:
   ret void
 }
 
+; Function Attrs: mustprogress nofree noinline norecurse nounwind ssp memory(readwrite, argmem: none) uwtable(sync)
+define void @func_call_thunked_1_nomerge() local_unnamed_addr #0 {
+entry:
+  tail call void @func_2identical_v1()
+  store volatile i8 77, ptr @g_val, align 1, !tbaa !5
+  ret void
+}
+
+; Function Attrs: mustprogress nofree noinline norecurse nounwind ssp memory(readwrite, argmem: none) uwtable(sync)
+define void @func_call_thunked_2_nomerge() local_unnamed_addr #0 {
+entry:
+  tail call void @func_2identical_v2()
+  store volatile i8 77, ptr @g_val, align 1, !tbaa !5
+  ret void
+}
+
+; Function Attrs: mustprogress nofree noinline norecurse nounwind ssp memory(readwrite, argmem: none) uwtable(sync)
+define void @func_call_thunked_2_merge() local_unnamed_addr #0 {
+entry:
+  tail call void @func_2identical_v2()
+  store volatile i8 77, ptr @g_val, align 1, !tbaa !5
+  ret void
+}
+
 ; Function Attrs: mustprogress nofree noinline norecurse nounwind ssp uwtable(sync)
 define void @call_all_funcs() local_unnamed_addr #1 {
 entry:
@@ -227,6 +261,21 @@ attributes #1 = { mustprogress nofree noinline norecurse nounwind ssp uwtable(sy
 ;     g_val = 33;
 ; }
 ;
+; ATTR void func_call_thunked_1_nomerge() {
+;     func_2identical_v1();
+;     g_val = 77;
+; }
+;
+; ATTR void func_call_thunked_2_nomerge() {
+;     func_2identical_v2();
+;     g_val = 77;
+; }
+;
+; ATTR void func_call_thunked_2_merge() {
+;     func_2identical_v2();
+;     g_val = 77;
+; }
+;
 ; ATTR void call_all_funcs() {
 ;     func_unique_1();
 ;     func_unique_2_canmerge();