[BOLT] Store FileSymRefs in a multimap

With aggressive ICF, it's possible to have different local symbols
(under different FILE symbols) to be mapped to the same address.

FileSymRefs only keeps a single SymbolRef per address, which prevents
fragment matching from finding the correct symbol to perform parent
function lookup.

Work around this issue by switching FileSymRefs to a multimap. In
future, uses of FileSymRefs can be replaced with SortedSymbols which
keeps essentially the same information.

Test Plan: added ambiguous_fragment.test

Reviewers: dcci, ayermolo, maksfb, rafaelauler

Reviewed By: rafaelauler

Pull Request: https://github.com/llvm/llvm-project/pull/98992

3 files changed, 93 insertions, 0 deletions

diff --git a/bolt/test/X86/Inputs/ambiguous_fragment.s b/bolt/test/X86/Inputs/ambiguous_fragment.s
new file mode 100644
index 0000000..05346ff
--- /dev/null
+++ b/bolt/test/X86/Inputs/ambiguous_fragment.s
@@ -0,0 +1,54 @@
+#--- file1
+.file "file1.cpp"
+.section .text.cold
+.type __func.cold.0, @function
+__func.cold.0:
+  ud2
+  .size __func.cold.0, .-__func.cold.0
+.section .text
+.type __func, @function
+__func:
+  ud2
+  .size __func, .-__func
+
+#--- file2
+.file "file2.cpp"
+.section .text.cold
+.type __func.cold.0, @function
+__func.cold.0:
+  ud2
+  .size __func.cold.0, .-__func.cold.0
+.section .text
+.type __func, @function
+__func:
+  ud2
+  .size __func, .-__func
+
+#--- file3
+.file "file3.cpp"
+.section .text.cold
+.type __func.cold.0, @function
+__func.cold.0:
+  ud2
+  .size __func.cold.0, .-__func.cold.0
+.section .text
+.type __func, @function
+__func:
+  ud2
+  .size __func, .-__func
+
+#--- file4
+.file "file4.cpp"
+.section .text.cold
+.type __func.cold.0, @function
+__func.cold.0:
+  ud2
+  .size __func.cold.0, .-__func.cold.0
+.section .text
+.type __func, @function
+__func:
+  ud2
+  .size __func, .-__func
+
+#--- file5
+.file "bolt-pseudo.o"
diff --git a/bolt/test/X86/Inputs/ambiguous_fragment.script b/bolt/test/X86/Inputs/ambiguous_fragment.script
new file mode 100644
index 0000000..00129b8
--- /dev/null
+++ b/bolt/test/X86/Inputs/ambiguous_fragment.script
@@ -0,0 +1,6 @@
+SECTIONS {
+  . = 0x10000;
+  .text : { *(.text) }
+  . = 0x20000;
+  .text.cold : { *(.text.cold) }
+}
diff --git a/bolt/test/X86/ambiguous_fragment.test b/bolt/test/X86/ambiguous_fragment.test
new file mode 100644
index 0000000..e7d32c0
--- /dev/null
+++ b/bolt/test/X86/ambiguous_fragment.test
@@ -0,0 +1,33 @@
+## This reproduces a bug with misidentification of a parent fragment.
+
+RUN: split-file %p/Inputs/ambiguous_fragment.s %t
+
+RUN: llvm-mc --filetype=obj --triple x86_64-unknown-unknown %t/file1 -o %t1.o
+RUN: llvm-mc --filetype=obj --triple x86_64-unknown-unknown %t/file2 -o %t2.o
+RUN: llvm-mc --filetype=obj --triple x86_64-unknown-unknown %t/file3 -o %t3.o
+RUN: llvm-mc --filetype=obj --triple x86_64-unknown-unknown %t/file4 -o %t4.o
+RUN: llvm-mc --filetype=obj --triple x86_64-unknown-unknown %t/file5 -o %t5.o
+
+RUN: ld.lld %t1.o %t2.o %t3.o %t4.o %t5.o -o %t.exe \
+RUN:   --script %p/Inputs/ambiguous_fragment.script
+
+RUN: llvm-objcopy %t.exe %t.exe2 \
+RUN:   --add-symbol=_Zfunc.cold.0=.text.cold:0x4,local,function \
+RUN:   --add-symbol=_Zfunc=.text:0xc,function
+
+RUN: llvm-objdump --syms %t.exe2 | FileCheck %s --check-prefix=CHECK-SYMS
+
+RUN: link_fdata %s %t.exe2 %t.preagg PREAGG
+RUN: perf2bolt -v=1 %t.exe2 -p %t.preagg --pa -o %t.fdata -w %t.yaml | FileCheck %s
+
+# PREAGG: B X:0 #__func# 1 0
+
+CHECK-SYMS: 0000000000020004 {{.*}} __func.cold.0
+CHECK-SYMS: 0000000000020004 {{.*}} _Zfunc.cold.0
+
+CHECK-NOT:  BOLT-ERROR: parent function not found for __func.cold.0
+CHECK:      BOLT-INFO: marking __func.cold.0/3(*4) as a fragment of __func/4(*3)
+CHECK-NEXT: BOLT-INFO: marking __func.cold.0/1(*2) as a fragment of __func/1(*2)
+CHECK-NEXT: BOLT-INFO: marking __func.cold.0/2(*2) as a fragment of __func/2(*2)
+CHECK-NEXT: BOLT-INFO: marking __func.cold.0/3(*4) as a fragment of __func/3(*2)
+CHECK-NEXT: BOLT-INFO: marking __func.cold.0/4(*2) as a fragment of __func/4(*3)