[BOLT][AArch64] Reduce the number of ADR relaxations (#111577)

If ADR instruction references the same function, we can skip relaxation
even if the function is split but ADR is in the main fragment.

Author: maksfb

bolt/lib/Passes/ADRRelaxationPass.cpp

@@ -56,13 +56,14 @@ void ADRRelaxationPass::runOnFunction(BinaryFunction &BF) {
           continue;
       }
 
-      // Don't relax adr if it points to the same function and it is not split
-      // and BF initial size is < 1MB.
+      // Don't relax ADR if it points to the same function and is in the main
+      // fragment and BF initial size is < 1MB.
       const unsigned OneMB = 0x100000;
       if (BF.getSize() < OneMB) {
         BinaryFunction *TargetBF = BC.getFunctionForSymbol(Symbol);
-        if (TargetBF == &BF && !BF.isSplit())
+        if (TargetBF == &BF && !BB.isSplit())
           continue;
+
         // No relaxation needed if ADR references a basic block in the same
         // fragment.
         if (BinaryBasicBlock *TargetBB = BF.getBasicBlockForLabel(Symbol))

bolt/test/AArch64/adr-relaxation.s

@@ -0,0 +1,49 @@
+## Check that llvm-bolt will not unnecessarily relax ADR instruction.
+
+# RUN: llvm-mc -filetype=obj -triple aarch64-unknown-unknown %s -o %t.o
+# RUN: %clang %cflags %t.o -o %t.exe -Wl,-q -static
+# RUN: llvm-bolt %t.exe -o %t.bolt --split-functions --split-strategy=random2
+# RUN: llvm-objdump -d --disassemble-symbols=_start %t.bolt | FileCheck %s
+# RUN: llvm-objdump -d --disassemble-symbols=foo.cold.0 %t.bolt \
+# RUN:   | FileCheck --check-prefix=CHECK-FOO %s
+
+## ADR below references its containing function that is split. But ADR is always
+## in the main fragment, thus there is no need to relax it.
+  .text
+  .globl _start
+  .type _start, %function
+_start:
+# CHECK: <_start>:
+  .cfi_startproc
+  adr x1, _start
+# CHECK-NOT: adrp
+# CHECK: adr
+  cmp  x1, x11
+  b.hi  .L1
+  mov  x0, #0x0
+.L1:
+  ret  x30
+  .cfi_endproc
+.size _start, .-_start
+
+
+## In foo, ADR is in the split fragment but references the main one. Thus, it
+## needs to be relaxed into ADRP + ADD.
+  .globl foo
+  .type foo, %function
+foo:
+  .cfi_startproc
+  cmp  x1, x11
+  b.hi  .L2
+  mov  x0, #0x0
+.L2:
+# CHECK-FOO: <foo.cold.0>:
+  adr x1, foo
+# CHECK-FOO: adrp
+# CHECK-FOO-NEXT: add
+  ret  x30
+  .cfi_endproc
+.size foo, .-foo
+
+## Force relocation mode.
+  .reloc 0, R_AARCH64_NONE