Incorrect function call code on ARMv6

On 2016-08-11 09:24 +0100, Balazs Kezes wrote:
> I think it's just that that copy_params() never restores the spilled
> registers. Maybe it needs some extra code at the end to see if any
> parameters have been spilled to stack and then restore them?

I've spent some time on this and I've found an alternative solution.
Although I'm not entirely sure about it but I've attached a patch
nevertheless.

And while poking at that I've found another problem affecting the
unsigned long long division on arm and I've attached a patch for that
too.

More details in the patches themselves. Please review and consider them
for merging! Thank you!

--
Balazs

[PATCH 1/2] Fix slow unsigned long long division on ARM

The macro AEABI_UXDIVMOD expands to this bit:

  #define AEABI_UXDIVMOD(name,type, rettype, typemacro)                     \
  ...
      while (num >= den) {                                                  \
  ...
          while ((q << 1) * den <= num && q * den <= typemacro ## _MAX / 2) \
              q <<= 1;                                                      \
  ...

With the current ULONG_MAX version the inner loop goes only until 4
billion so the outer loop will progress very slowly if num is large.
With ULLONG_MAX the inner loop works as expected. The current version is
probably a result of a typo.

The following bash snippet demonstrates the bug:

  $ uname -a
  Linux eper 4.4.16-2-ARCH #1 Wed Aug 10 20:03:13 MDT 2016 armv6l GNU/Linux
  $ cat div.c
  int printf(const char *, ...);
  int main(void) {
    unsigned long long num, denom;
    num = 12345678901234567ULL;
    denom = 7;
    printf("%lld\n", num / denom);
    return 0;
  }
  $ time tcc -run div.c
  1763668414462081

  real    0m16.291s
  user    0m15.860s
  sys     0m0.020s

[PATCH 2/2] Fix long long dereference during argument passing on ARMv6

For some reason the code spills the register to the stack. copy_params
in arm-gen.c doesn't expect this so bad code is generated. It's not
entirely clear why the saving part is necessary. It was added in commit
59c35638 with the comment "fixed long long code gen bug" with no further
clarification. Given that tcctest.c passes without this, maybe it's no
longer needed? Let's remove it.

Also add a new testcase just for this. After I've managed to make the
tests compile on a raspberry pi, I get the following diff without this
patch:

  --- test.ref    2016-08-22 22:12:43.380000000 +0100
  +++ test.out3   2016-08-22 22:12:49.990000000 +0100
  @@ -499,7 +499,7 @@
   2
   1 0 1 0
   4886718345
  -shift: 9 9 9312
  +shift: 291 291 291
   shiftc: 36 36 2328
   shiftc: 0 0 9998683865088
   manyarg_test:

More discussion on this thread:
https://lists.nongnu.org/archive/html/tinycc-devel/2016-08/msg00004.html

lib/armeabi.c

@@ -399,7 +399,7 @@ REGS_RETURN(ulldiv_t, ulldiv_t)
 REGS_RETURN(idiv_t, idiv_t)
 REGS_RETURN(uidiv_t, uidiv_t)
 
-AEABI_UXDIVMOD(uldivmod, unsigned long long, ulldiv_t, ULONG)
+AEABI_UXDIVMOD(uldivmod, unsigned long long, ulldiv_t, ULLONG)
 
 __AEABI_XDIVMOD(ldivmod, long long, uldivmod, lldiv_t, ulldiv_t, LLONG)
 

tccgen.c

@@ -861,11 +861,6 @@ ST_FUNC int gv(int rc)
 #endif
                 if (r >= VT_CONST || /* XXX: test to VT_CONST incorrect ? */
                            (vtop->r & VT_LVAL)) {
-                    /* We do not want to modifier the long long
-                       pointer here, so the safest (and less
-                       efficient) is to save all the other registers
-                       in the stack. XXX: totally inefficient. */
-                    save_regs(1);
                     /* load from memory */
                     vtop->type.t = load_type;
                     load(r, vtop);

tests/tcctest.c

@@ -2010,6 +2010,11 @@ void longlong_test(void)
     printf("%d %d %d %d\n", a > b, a < b, a >= b, a <= b);
 
     printf(LONG_LONG_FORMAT "\n", 0x123456789LLU);
+
+    /* long long pointer deref in argument passing test */
+    a = 0x123;
+    long long *p = &a;
+    llshift(*p, 5);
 }
 
 void manyarg_test(void)