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LLVM backend for 6502
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43a6c5e2fc
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Bill Wendling 43a6c5e2fc We have a chance for an optimization. Consider this code: 
int x(int t) {
  if (t & 256)
    return -26;
  return 0;
}

We generate this:

     tst.w   r0, #256
     mvn     r0, #25
     it      eq
     moveq   r0, #0

while gcc generates this:

     ands    r0, r0, #256
     it      ne
     mvnne   r0, #25
     bx      lr

Scandalous really!

During ISel time, we can look for this particular pattern. One where we have a
"MOVCC" that uses the flag off of a CMPZ that itself is comparing an AND
instruction to 0. Something like this (greatly simplified):

  %r0 = ISD::AND ...
  ARMISD::CMPZ %r0, 0         @ sets [CPSR]
  %r0 = ARMISD::MOVCC 0, -26  @ reads [CPSR]

All we have to do is convert the "ISD::AND" into an "ARM::ANDS" that sets [CPSR]
when it's zero. The zero value will all ready be in the %r0 register and we only
need to change it if the AND wasn't zero. Easy!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112664 91177308-0d34-0410-b5e6-96231b3b80d8
2010-08-31 22:41:22 +00:00
autoconf Fix LLVM target initialization to deal with sociopathic outside projects 2010-08-30 18:34:48 +00:00
bindings Remove unions from the ocaml bindings. 2010-08-28 09:47:42 +00:00
cmake Fix LLVM target initialization to deal with sociopathic outside projects 2010-08-30 18:34:48 +00:00
docs Stack slot access methods are in TargetInstrInfo. 2010-08-31 22:01:07 +00:00
examples Remove this from the main tree. I'll host it out of tree. 2010-08-30 21:34:26 +00:00
include Reapply r112623. Included additional check for unused byval argument. 2010-08-31 22:22:42 +00:00
lib We have a chance for an optimization. Consider this code: 2010-08-31 22:41:22 +00:00
projects Remove bogus link. 2010-07-16 06:33:36 +00:00
runtime Delete a blank line. 2010-04-16 13:32:55 +00:00
test We have a chance for an optimization. Consider this code: 2010-08-31 22:41:22 +00:00
tools Cleanup Whitespace. 2010-08-31 06:36:46 +00:00
unittests StringRef::compare_numeric also differed from StringRef::compare for characters > 127. 2010-08-26 15:25:35 +00:00
utils Don't worry about union types. 2010-08-29 14:50:21 +00:00
website
build-for-llvm-top.sh
CMakeLists.txt Attempt to remove the MSIL backend from CMake as well based on Chris's r112375. 2010-08-30 07:25:54 +00:00
configure Fix LLVM target initialization to deal with sociopathic outside projects 2010-08-30 18:34:48 +00:00
CREDITS.TXT Flesh out the list of things I've worked on. 2010-08-29 04:22:35 +00:00
LICENSE.TXT
llvm.spec.in
Makefile llvmc: remove dynamic plugins. 2010-08-15 07:07:12 +00:00
Makefile.common
Makefile.config.in Make the makefiles go much faster by using the realpath 2010-08-03 22:53:22 +00:00
Makefile.rules Fix the "Finished Creating" messages for aliases to print the 2010-08-18 01:35:53 +00:00
ModuleInfo.txt
README.txt (Hopefully) One last test. 2010-07-27 00:04:55 +00:00

README.txt 

\Low Level Virtual Machine (LLVM)
================================

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