[BOLT] Allow builtin_unreachable to be at MaxSize address

[aaupov]

Lift the restriction that builtin_unreachable has to be strictly within
MaxSize of a function.

Test Plan: added builtin_unreachable.s

[llvmbot]

@llvm/pr-subscribers-bolt

Author: Amir Ayupov (aaupov)

Changes

Lift the restriction that builtin_unreachable has to be strictly within
MaxSize of a function.

Test Plan: added builtin_unreachable.s

---

Full diff: https://github.com/llvm/llvm-project/pull/111771.diff

2 Files Affected:

• (modified) bolt/lib/Core/BinaryFunction.cpp (+3-2)
• (added) bolt/test/X86/builtin_unreachable.s (+33)

diff --git a/bolt/lib/Core/BinaryFunction.cpp b/bolt/lib/Core/BinaryFunction.cpp
index 27c8ccefedee10..8b1f441a3a01da 100644
--- a/bolt/lib/Core/BinaryFunction.cpp
+++ b/bolt/lib/Core/BinaryFunction.cpp
@@ -1365,8 +1365,9 @@ Error BinaryFunction::disassemble() {
           if (containsAddress(TargetAddress)) {
             TargetSymbol = getOrCreateLocalLabel(TargetAddress);
           } else {
-            if (TargetAddress == getAddress() + getSize() &&
-                TargetAddress < getAddress() + getMaxSize() &&
+            if (BC.isELF() && !BC.getBinaryDataAtAddress(TargetAddress) &&
+                TargetAddress == getAddress() + getSize() &&
+                TargetAddress <= getAddress() + getMaxSize() &&
                 !(BC.isAArch64() &&
                   BC.handleAArch64Veneer(TargetAddress, /*MatchOnly*/ true))) {
               // Result of __builtin_unreachable().
diff --git a/bolt/test/X86/builtin_unreachable.s b/bolt/test/X86/builtin_unreachable.s
new file mode 100644
index 00000000000000..ab533629d1a846
--- /dev/null
+++ b/bolt/test/X86/builtin_unreachable.s
@@ -0,0 +1,33 @@
+## Check that BOLT properly identifies a jump to builtin_unreachable
+
+# RUN: llvm-mc -filetype=obj -triple x86_64-unknown-unknown %s -o %t.o
+# RUN: ld.lld -q -o %t %t.o
+# RUN: llvm-bolt %t -o %t.null -lite=0 -print-disasm | FileCheck %s
+# CHECK:      callq bar
+# CHECK-NEXT: nop
+
+.text
+.globl main
+.type main, @function
+main:
+  call foo
+  .size main, .-main
+
+.section .mytext.bar, "ax"
+.globl  bar
+.type	bar, @function
+bar:
+  ud2
+	.size	bar, .-bar
+
+.section .mytext.foo, "ax"
+.globl	foo
+.type	foo, @function
+foo:
+.cfi_startproc
+  callq bar
+  jmp .Lunreachable
+  ret
+  .cfi_endproc
+	.size	foo, .-foo
+.Lunreachable:

[maksfb]

What happens when there's a data object at TargetAddress?