[BOLT][AArch64] Fixes assertion errors occurred when perf2bolt was executed (#83394)

BOLT only checks for the most common indirect branch pattern during the
branch analyzation.
Extended the logic with two other indirect patterns which slightly
differ from the expected one.
Those patterns may be hit when statically linking libc (pattern 2
requires 'lld' linker).

As a workaround mark them as UNKNOWN branch for now. 

Fixes: #83114

Author: kaadam

bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp

@@ -702,8 +702,20 @@ class AArch64MCPlusBuilder : public MCPlusBuilder {
     unsigned ShiftVal = AArch64_AM::getArithShiftValue(OperandExtension);
     AArch64_AM::ShiftExtendType ExtendType =
         AArch64_AM::getArithExtendType(OperandExtension);
-    if (ShiftVal != 2)
-      llvm_unreachable("Failed to match indirect branch! (fragment 2)");
+    if (ShiftVal != 2) {
+      // TODO: Handle the patten where ShiftVal != 2.
+      // The following code sequence below has no shift amount,
+      // the range could be 0 to 4.
+      // The pattern comes from libc, it occurs when the binary is static.
+      //   adr     x6, 0x219fb0 <sigall_set+0x88>
+      //   add     x6, x6, x14, lsl #2
+      //   ldr     w7, [x6]
+      //   add     x6, x6, w7, sxtw => no shift amount
+      //   br      x6
+      errs() << "BOLT-WARNING: "
+                "Failed to match indirect branch: ShiftVAL != 2 \n";
+      return false;
+    }
 
     if (ExtendType == AArch64_AM::SXTB)
       ScaleValue = 1LL;
@@ -748,6 +760,19 @@ class AArch64MCPlusBuilder : public MCPlusBuilder {
       return true;
     }
 
+    if (DefJTBaseAdd->getOpcode() == AArch64::ADR) {
+      // TODO: Handle the pattern where there is no adrp/add pair.
+      // It also occurs when the binary is static.
+      //  adr     x13, 0x215a18 <_nl_value_type_LC_COLLATE+0x50>
+      //  ldrh    w13, [x13, w12, uxtw #1]
+      //  adr     x12, 0x247b30 <__gettextparse+0x5b0>
+      //  add     x13, x12, w13, sxth #2
+      //  br      x13
+      errs() << "BOLT-WARNING: Failed to match indirect branch: "
+                "nop/adr instead of adrp/add \n";
+      return false;
+    }
+
     assert(DefJTBaseAdd->getOpcode() == AArch64::ADDXri &&
            "Failed to match jump table base address pattern! (1)");
 

bolt/test/AArch64/test-indirect-branch.s

@@ -0,0 +1,83 @@
+// Test how BOLT handles indirect branch sequence of instructions in
+// AArch64MCPlus builder.
+
+// clang-format off
+
+// REQUIRES: system-linux
+// RUN: llvm-mc -filetype=obj -triple aarch64-unknown-unknown %s -o %t.o
+// RUN: %clang %cflags --target=aarch64-unknown-linux %t.o -o %t.exe -Wl,-q
+// RUN: llvm-bolt %t.exe -o %t.bolt --print-cfg --strict\
+// RUN:  -v=1 2>&1 | FileCheck %s
+
+// Pattern 1: there is no shift amount after the 'add' instruction.
+//
+//   adr     x6, 0x219fb0 <sigall_set+0x88>
+//   add     x6, x6, x14, lsl #2
+//   ldr     w7, [x6]
+//   add     x6, x6, w7, sxtw => no shift amount
+//   br      x6
+//
+
+// Pattern 2: nop/adr pair is used in place of adrp/add
+//
+//  nop   => nop/adr instead of adrp/add
+//  adr     x13, 0x215a18 <_nl_value_type_LC_COLLATE+0x50>
+//  ldrh    w13, [x13, w12, uxtw #1]
+//  adr     x12, 0x247b30 <__gettextparse+0x5b0>
+//  add     x13, x12, w13, sxth #2
+//  br      x13
+
+  .section .text
+  .align 4
+  .globl _start
+  .type  _start, %function
+_start:
+  bl      test1
+  bl      test2
+// mov x0, #4
+// mov w8, #93
+// svc #0
+
+// Pattern 1
+// CHECK: BOLT-WARNING: Failed to match indirect branch: ShiftVAL != 2
+  .globl test1
+  .type  test1, %function
+test1:
+  mov     x1, #0
+  adr     x3, datatable
+  add     x3, x3, x1, lsl #2
+  ldr     w2, [x3]
+  add     x3, x3, w2, sxtw
+  br      x3
+test1_0:
+   ret
+test1_1:
+   ret
+test1_2:
+   ret
+
+// Pattern 2
+// CHECK: BOLT-WARNING: Failed to match indirect branch: nop/adr instead of adrp/add
+  .globl test2
+  .type  test2, %function
+test2:
+  nop
+  adr     x3, jump_table
+  ldrh    w3, [x3, x1, lsl #1]
+  adr     x1, test2_0
+  add     x3, x1, w3, sxth #2
+  br      x3
+test2_0:
+  ret
+test2_1:
+  ret
+
+  .section .rodata,"a",@progbits
+datatable:
+  .word test1_0-datatable
+  .word test1_1-datatable
+  .word test1_2-datatable
+
+jump_table:
+  .hword  (test2_0-test2_0)>>2
+  .hword  (test2_1-test2_0)>>2