[Builtins] Fix div0 error in udivsi3

[weimingz]

Summary

Need to save lr before bl to aeabi_div0

[compnerd]

lib/builtins/arm/udivsi3.S

198

Why r6 and not r7? That would be the FP, and saving that makes stack walking better.

[weimingz]

I think the r7 (fp) was not set to initial SP, so it won't matter for stack-based unwinding. Anyway, use r7 now.

[weimingz]

move up the "divby0" block for the case with HW div to make the code easier to read.

lib/builtins/arm/udivsi3.S

 #else
 DEFINE_COMPILERRT_FUNCTION(__udivsi3)
 #endif
 #if __ARM_ARCH_EXT_IDIV__
   tst     r1, r1
   beq     LOCAL_LABEL(divby0)
   udiv  r0, r0, r1
   bx    lr
-#else
+
+LOCAL_LABEL(divby0):
+  mov     r0, #0
+#  ifdef __ARM_EABI__
+  b       __aeabi_idiv0
+#  else
+  JMP(lr)
+#  endif
+
+#else /* ! __ARM_ARCH_EXT_IDIV__ */
   cmp r1, #1
   bcc LOCAL_LABEL(divby0)
 #if __ARM_ARCH_ISA_THUMB == 1
   bne LOCAL_LABEL(num_neq_denom)
   JMP(lr)
 LOCAL_LABEL(num_neq_denom):
 #else
   IT(eq)

 
 
 #define IMM #
   /* due to the range limit of branch in Thumb1, we have to place the
      block closer */
 LOCAL_LABEL(divby0):
   movs  r0, #0
 #      if defined(__ARM_EABI__)
+  push {r7, lr}
   bl  __aeabi_idiv0 // due to relocation limit, can't use b.
-#      endif
+  pop  {r7, pc}
+#      else
   JMP(lr)
+#      endif
 
 
 #if __ARM_ARCH_ISA_THUMB == 1
 #define block(shift)                                                           \
   lsls r2, r1, IMM shift;                                                      \
   cmp r0, r2;                                                                  \
   blo LOCAL_LABEL(block_skip_##shift);                                         \
   subs r0, r0, r2;                                                             \
#endif
   block(1)
 LOCAL_LABEL(div0block):
   block(0)
 
   mov r0, r3
   JMP(lr)
 #endif /* __ARM_ARCH_EXT_IDIV__ */
 
-#if __ARM_ARCH_EXT_IDIV__
-LOCAL_LABEL(divby0):
-        mov     r0, #0
-#  ifdef __ARM_EABI__
-        b       __aeabi_idiv0
-#  else
-        JMP(lr)
-#  endif
-#endif
-
 END_COMPILERRT_FUNCTION(__udivsi3)
 
 NO_EXEC_STACK_DIRECTIVE