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LLVM backend for 6502
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Evan Cheng 66ac53165e Change Thumb2 jumptable codegen to one that uses two level jumps: 
Before:
      adr r12, #LJTI3_0_0
      ldr pc, [r12, +r0, lsl #2]
LJTI3_0_0:
      .long    LBB3_24
      .long    LBB3_30
      .long    LBB3_31
      .long    LBB3_32

After:
      adr r12, #LJTI3_0_0
      add pc, r12, +r0, lsl #2
LJTI3_0_0:
      b.w    LBB3_24
      b.w    LBB3_30
      b.w    LBB3_31
      b.w    LBB3_32

This has several advantages.
1. This will make it easier to optimize this to a TBB / TBH instruction +
   (smaller) table.
2. This eliminate the need for ugly asm printer hack to force the address
   into thumb addresses (bit 0 is one).
3. Same codegen for pic and non-pic.
4. This eliminate the need to align the table so constantpool island pass
   won't have to over-estimate the size.

Based on my calculation, the later is probably slightly faster as well since
ldr pc with shifter address is very slow. That is, it should be a win as long
as the HW implementation can do a reasonable job of branch predict the second
branch.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@77024 91177308-0d34-0410-b5e6-96231b3b80d8
2009-07-25 00:33:29 +00:00
autoconf
bindings
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docs Tweak, raw_ostream is a ostream, not iostream replacement 2009-07-24 23:54:34 +00:00
examples Revert the ConstantInt constructors back to their 2.5 forms where possible, thanks to contexts-on-types. More to come. 2009-07-24 23:12:02 +00:00
include MemoryObject - Abstract base class for contiguous addressable memory. 2009-07-25 00:30:51 +00:00
lib Change Thumb2 jumptable codegen to one that uses two level jumps: 2009-07-25 00:33:29 +00:00
projects
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test Change Thumb2 jumptable codegen to one that uses two level jumps: 2009-07-25 00:33:29 +00:00
tools Revert the ConstantInt constructors back to their 2.5 forms where possible, thanks to contexts-on-types. More to come. 2009-07-24 23:12:02 +00:00
unittests Revert the ConstantInt constructors back to their 2.5 forms where possible, thanks to contexts-on-types. More to come. 2009-07-24 23:12:02 +00:00
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win32 Revert the ConstantInt constructors back to their 2.5 forms where possible, thanks to contexts-on-types. More to come. 2009-07-24 23:12:02 +00:00
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