[llvm] [BOLT][AArch64] Do not relax ADR referencing the same fragment (PR #108673)

[Maksim Panchenko via llvm-commits]

https://github.com/maksfb created https://github.com/llvm/llvm-project/pull/108673

ADR can reference a secondary entry point in the same function. If that's the case, we can skip relaxing the instruction when it is in the same fragment as its target.

Fixes #108290

>From 9418322643a3fbc02c3358564b1420a6f3b49f5a Mon Sep 17 00:00:00 2001
From: Maksim Panchenko <maks at fb.com>
Date: Fri, 13 Sep 2024 20:06:19 -0700
Subject: [PATCH] [BOLT][AArch64] Do not relax ADR referencing the same
 fragment

ADR can reference a secondary entry point in the same function. If
that's the case, we can skip relaxing the instruction when it is in the
same fragment as its target.

Fixes #108290
---
 bolt/lib/Passes/ADRRelaxationPass.cpp | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/bolt/lib/Passes/ADRRelaxationPass.cpp b/bolt/lib/Passes/ADRRelaxationPass.cpp
index 24fddbc764cbe7..256034a841c706 100644
--- a/bolt/lib/Passes/ADRRelaxationPass.cpp
+++ b/bolt/lib/Passes/ADRRelaxationPass.cpp
@@ -59,10 +59,15 @@ void ADRRelaxationPass::runOnFunction(BinaryFunction &BF) {
       // Don't relax adr if it points to the same function and it is not split
       // and BF initial size is < 1MB.
       const unsigned OneMB = 0x100000;
-      if (!BF.isSplit() && BF.getSize() < OneMB) {
+      if (BF.getSize() < OneMB) {
         BinaryFunction *TargetBF = BC.getFunctionForSymbol(Symbol);
-        if (TargetBF && TargetBF == &BF)
+        if (TargetBF == &BF && !BF.isSplit())
           continue;
+        // No relaxation needed if ADR references a basic block in the same
+        // fragment.
+        if (BinaryBasicBlock *TargetBB = BF.getBasicBlockForLabel(Symbol))
+          if (BB.getFragmentNum() == TargetBB->getFragmentNum())
+            continue;
       }
 
       MCPhysReg Reg;