[llvm] [BOLT] Keep multi-entry functions simple in aggregation mode (PR #128253)

[Amir Ayupov via llvm-commits]

https://github.com/aaupov created https://github.com/llvm/llvm-project/pull/128253

BOLT used to mark multi-entry functions non-simple in non-relocation
mode with the reasoning that we can't move them due to potentially
undetected references. However, in aggregation mode it doesn't apply as
BOLT doesn't perform optimizations.

Relax this constraint in case of an aggregation job.

Test Plan: added entry-point-fallthru.s


>From 7ae2b1ea4672b2fd1605a0b9b879aac2c4e64219 Mon Sep 17 00:00:00 2001
From: Amir Ayupov <aaupov at fb.com>
Date: Fri, 21 Feb 2025 15:59:49 -0800
Subject: [PATCH] =?UTF-8?q?[=F0=9D=98=80=F0=9D=97=BD=F0=9D=97=BF]=20initia?=
 =?UTF-8?q?l=20version?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Created using spr 1.3.4
---
 bolt/lib/Core/BinaryFunction.cpp     |  5 +++--
 bolt/test/X86/entry-point-fallthru.s | 24 ++++++++++++++++++++++++
 2 files changed, 27 insertions(+), 2 deletions(-)
 create mode 100644 bolt/test/X86/entry-point-fallthru.s

diff --git a/bolt/lib/Core/BinaryFunction.cpp b/bolt/lib/Core/BinaryFunction.cpp
index 8385551576098..ff5eb5cf6e1eb 100644
--- a/bolt/lib/Core/BinaryFunction.cpp
+++ b/bolt/lib/Core/BinaryFunction.cpp
@@ -15,6 +15,7 @@
 #include "bolt/Core/DynoStats.h"
 #include "bolt/Core/HashUtilities.h"
 #include "bolt/Core/MCPlusBuilder.h"
+#include "bolt/Utils/CommandLineOpts.h"
 #include "bolt/Utils/NameResolver.h"
 #include "bolt/Utils/NameShortener.h"
 #include "bolt/Utils/Utils.h"
@@ -1753,8 +1754,8 @@ void BinaryFunction::postProcessEntryPoints() {
     // In non-relocation mode there's potentially an external undetectable
     // reference to the entry point and hence we cannot move this entry
     // point. Optimizing without moving could be difficult.
-    // In BAT mode, register any known entry points for CFG construction.
-    if (!BC.HasRelocations && !BC.HasBATSection)
+    // In aggregation, register any known entry points for CFG construction.
+    if (!BC.HasRelocations && !opts::AggregateOnly)
       setSimple(false);
 
     const uint32_t Offset = KV.first;
diff --git a/bolt/test/X86/entry-point-fallthru.s b/bolt/test/X86/entry-point-fallthru.s
new file mode 100644
index 0000000000000..edf14247b0c43
--- /dev/null
+++ b/bolt/test/X86/entry-point-fallthru.s
@@ -0,0 +1,24 @@
+## Checks that fallthroughs spanning entry points are accepted in aggregation
+## mode.
+
+# RUN: llvm-mc -filetype=obj -triple x86_64-unknown-unknown %s -o %t.o
+# RUN: ld.lld %t.o -o %t
+# RUN: link_fdata %s %t %t.preagg PREAGG
+# RUN: perf2bolt %t -p %t.preagg --pa -o %t.fdata | FileCheck %s
+# CHECK: traces mismatching disassembled function contents: 0
+
+	.globl main
+main:
+	.cfi_startproc
+	vmovaps %zmm31,%zmm3
+
+next:
+	add    $0x4,%r9
+	add    $0x40,%r10
+	dec    %r14
+Ljmp:
+	jne    main
+# PREAGG: T #Ljmp# #main# #Ljmp# 1
+	ret
+	.cfi_endproc
+.size main,.-main