[Bug target/44364] Wrong code with e500 double floating point

["Kyle dot D dot Moffett at boeing dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #3 from Kyle dot D dot Moffett at boeing dot com  2010-06-03 19:26 -------
(In reply to comment #0)
> So after looking at the code I saw now the following:
> 10000c24 <__floatdidf>:
> 10000c6c:       11 23 1a 2c     evmergehi r9,r3,r3
> 
> This function is touching the complete 64bit r9 register
> The code which calls it:
> 
> 10000a40:       91 21 00 20     stw     r9,32(r1)
> 10000a44:       4e 80 04 21     bctrl   # tell function which in turn calls
> floatdidf
> 
> 10000a7c:       81 21 00 20     lwz     r9,32(r1)
> 10000a80:       38 60 00 00     li      r3,0    
> 10000a84:       7e 33 8b 78     mr      r19,r17 
> 10000a88:       12 49 92 e1     efdsub  r18,r9,r18
> 10000a8c:       10 80 92 fa     efdctsiz r4,r18
> 10000a90:       12 49 4a 17     evmr    r18,r9  
> 
> So we just save the lower 32bit of r9 before calling the function and the upper
> 32bit are overwritten by efdsub.

Ok, here's the e500 ABI user guide:
  http://www.freescale.com/files/32bit/doc/ref_manual/E500ABIUG.pdf

According to that guide, we have the following usage of GPRs:
  Dedicated: r1 r2 r13
  Nonvolatile: r14-r31
  Volatile: r0 r3-r12

Then:
  Before a function changes the value in the upper word of any nonvolatile
general register, rn, it shall save the 64-bit value in rn in the 64-bit
general register save area 8*(32-n) bytes below the CR save area (plus any
required padding).  The 64-bit general save area shall have 8-byte alignment.

And:
  Before a function changes the value in the lower word of any nonvolatile
general register, rn, that has not already been saved in the 64-bit general
register save area, it shall save the value in the lower word of rn in the word
in the 32-bit general register save area 4*(32-n) bytes before the back chain
word of the previous frame.

So clearly the caller's assembly is wrong; it should be saving all 64-bits of
r9 (volatile gpr) first.

Cheers,
Kyle Moffett


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44364