[MIPS] Modify LongBranch expansion to work with sandboxing

test/MC/Mips/nacl-long-branch.ll

+; RUN: llc -filetype=obj -sfi-load -sfi-store -sfi-stack -sfi-branch -sfi-data \
+; RUN:     -force-mips-long-branch -O3 -mtriple mipsel-none-nacl %s -o - \
+; RUN:     | llvm-objdump -triple mipsel -disassemble -no-show-raw-insn - \
+; RUN:     | FileCheck %s
+
+; RUN: llc -filetype=obj -O3 -mtriple mipsel-none-nacl %s -o - \
+; RUN:     | llvm-objdump -triple mipsel -disassemble -no-show-raw-insn - \
+; RUN:     | FileCheck %s -check-prefix=CHECK-NOSFI
+
+
+declare void @f()
+
+define void @long_branch(i32 %arg) {
+entry:
+  %cmp = icmp eq i32 %arg, 0
+  br i1 %cmp, label %if.then, label %if.end
+if.then:
+  tail call void @f()
+  br label %if.end
+if.end:
+  ret void
+}
+
+; This file tests that MipsLongBranchPass works with sandboxing.
+; The nonsandboxed code of the previous function is:
+
+; long_branch:
+; CHECK-NOSFI:      0:       lui     $2, 0
+; CHECK-NOSFI:      4:       addiu   $2, $2, 0
+; CHECK-NOSFI:      8:       addiu   $sp, $sp, -24
+; CHECK-NOSFI:      c:       sw      $ra, 20($sp)
+; CHECK-NOSFI:     10:       bne     $4, $zero, 20
+; CHECK-NOSFI:     14:       addu    $gp, $2, $25
+; CHECK-NOSFI:     18:       lw      $25, 0($gp)
+; CHECK-NOSFI:     1c:       jalr    $25
+; CHECK-NOSFI:     20:       nop
+; CHECK-NOSFI:     24:       lw      $ra, 20($sp)
+; CHECK-NOSFI:     28:       addiu   $sp, $sp, 24
+; CHECK-NOSFI:     2c:       jr      $ra
+; CHECK-NOSFI:     30:       nop
+
+; We pass -force-mips-long-branch option to llc to make sure that bne
+; instruction is expanded into long branch. We specifically test that
+; in the expanded sandboxed long branch sequence the offset that LUi/ADDiu
+; instructions create is the correct offset from the ADDiu instruction to the
+; branch target (which is lw $ra, 20($sp) in this case). More precisely:
+;
+;   0x80 - 0x40 = 64,
+; where 0x40 and 0x80 are addresses and 64 is in the "addiu" at 0x40.
+
+;                0:       lui     $2, 0
+;                4:       addiu   $2, $2, 0
+;                8:       addiu   $sp, $sp, -24
+;                c:       and     $sp, $sp, $15
+;               10:       sw      $ra, 20($sp)
+;               14:       beq     $4, $zero, 80
+;               18:       addu    $gp, $2, $25
+;               1c:       nop
+;               20:       addiu   $sp, $sp, -8
+;               24:       and     $sp, $sp, $15
+;               28:       sw      $ra, 0($sp)
+;               2c:       nop
+;               30:       nop
+;               34:       nop
+; CHECK:        38:       bal     8
+; CHECK-NEXT:   3c:       lui     $1, 0
+; CHECK-NEXT:   40:       addiu   $1, $1, 64
+; CHECK:                  addu    $1, $ra, $1
+; CHECK:                  lw      $ra, 0($sp)
+; CHECK:                  nop
+; CHECK:                  addiu   $sp, $sp, 8
+; CHECK:                  and     $sp, $sp, $15
+; CHECK:                  and     $1, $1, $14
+; CHECK:                  jr      $1
+; CHECK:                  nop
+;               64:       and     $gp, $gp, $15
+;               68:       lw      $25, 0($gp)
+;               6c:       nop
+;               70:       nop
+;               74:       and     $25, $25, $14
+;               78:       jalr    $25
+;               7c:       nop
+; CHECK:        80:       lw      $ra, 20($sp)
+;               84:       addiu   $sp, $sp, 24
+;               88:       and     $sp, $sp, $15
+;               8c:       nop
+;               90:       and     $ra, $ra, $14
+;               94:       jr      $ra
+;               98:       nop