[gcc] Fix optimized expand of ptr diff for 64-bit PIC

[gcc] Fix optimized expand of ptr diff for 64-bit PIC

SImode subtraction instructions use "m" contstraint for one operand and "i" constraint for another. This does not work in 64-bit PIC in nacl, as "i" allows symbol references which get rip-relative addressing.

This replaces "i" constraint with "e" contraint, where the latter does not allow symbol references except those that simply fit in 32-bits immediate.

[khimg, 2010-08-23 11:59:31]

I like the description - it's as cryptic as it gets. Even after you take a look
on the patch itself it's not clear what it should fix and why.

Double-bonus for the fact that it changes non-nacl part of .md

But looks like it's tradition for GCC patches in general, so LGTM...

[eaeltsin, 2010-08-23 12:15:25]

OK, Victor, you are right, description sucks.
Fixed it together with patch comment.

Unfortunately we can't avoid touching non-nacl part of machine description, as
it does not fit ILP32 in x86_64.

[pasko-google - do not use, 2010-08-23 12:22:49]

I suspect this may degrade performance of the non-nacl GCC. Can we make specific
machine descriptions for ILP32?

[khimg, 2010-08-23 12:29:23]

2Egor: good idea. We can mark "normal" commands with !TARGET_NACL
and add different TARGET_NACL ones with different constraints.

Or perhaps even allow "normal" commands for IA32 nacl and "special" ones for
TARGET_NACL && TARGET_64BIT ...

[Mark Seaborn, 2010-08-23 13:06:20]

In the commit message please:
 * Link to the NaCl issue.
 * Say how it was tested.  You can put the small C test case in the commit
message.

Mark