Add a avoidWriteAfterWrite() target hook to identify register classes that
suffer from write-after-write hazards. For those register classes, try to avoid
writing the same register in two consecutive instructions.
This is currently disabled by default. We should not spill to avoid hazards!
The command line flag -avoid-waw-hazard can be used to enable waw avoidance.
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the generated FastISel. X86 doesn't need to generate code to match ADD16ri8
since ADD16ri will do just fine. This is a small codesize win in the generated
instruction selector.
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kind of predicate: one that is specific to imm nodes. The predicate function
specified here just checks an int64_t directly instead of messing around with
SDNode's. The virtue of this is that it means that fastisel and other things
can reason about these predicates.
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structure and fix some fixmes. We now have a TreePredicateFn class
that handles all of the decoding of these things. This is an internal
cleanup that has no impact on the code generated by tblgen.
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The basic issue here is that bottom-up isel is matching the branch
and compare, and was failing to fold the load into the branch/compare
combo. Fixing this (by allowing folding into any instruction of a
sequence that is selected) allows us to produce things like:
cmpb $0, 52(%rax)
je LBB4_2
instead of:
movb 52(%rax), %cl
cmpb $0, %cl
je LBB4_2
This makes the generated -O0 code run a bit faster, but also speeds up
compile time by putting less pressure on the register allocator and
generating less code.
This was one of the biggest classes of missing load folding. Implementing
this shrinks 176.gcc's c-decl.s (as a random example) by about 4% in (verbose-asm)
line count.
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does. Also mostly implement it. Still a work-in-progress, but generates legal
output on crafted test cases.
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Change ELF systems to use CFI for producing the EH tables. This reduces the
size of the clang binary in Debug builds from 690MB to 679MB.
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This is done by pushing physical register definitions close to their
use, which happens to handle flag definitions if they're not glued to
the branch. This seems to be generally a good thing though, so I
didn't need to add a target hook yet.
The primary motivation is to generate code closer to what people
expect and rule out missed opportunity from enabling macro-op
fusion. As a side benefit, we get several 2-5% gains on x86
benchmarks. There is one regression:
SingleSource/Benchmarks/Shootout/lists slows down be -10%. But this is
an independent scheduler bug that will be tracked separately.
See rdar://problem/9283108.
Incidentally, pre-RA scheduling is only half the solution. Fixing the
later passes is tracked by:
<rdar://problem/8932804> [pre-RA-sched] on x86, attempt to schedule CMP/TEST adjacent with condition jump
Fixes:
<rdar://problem/9262453> Scheduler unnecessary break of cmp/jump fusion
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will allow multiple context with different loop unroll parameters to run. This is a minor change and no effect
on existing application.
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Additional fixes:
Do something reasonable for subtargets with generic
itineraries by handle node latency the same as for an empty
itinerary. Now nodes default to unit latency unless an itinerary
explicitly specifies a zero cycle stage or it is a TokenFactor chain.
Original fixes:
UnitsSharePred was a source of randomness in the scheduler: node
priority depended on the queue data structure. I rewrote the recent
VRegCycle heuristics to completely replace the old heuristic without
any randomness. To make the ndoe latency adjustments work, I also
needed to do something a little more reasonable with TokenFactor. I
gave it zero latency to its consumers and always schedule it as low as
possible.
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Now that we have a first-class way to represent unaligned loads, the unaligned
load intrinsics are superfluous.
First part of <rdar://problem/8460511>.
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Add handling for tracking the relocations on symbols and resolving them.
Keep track of the relocations even after they are resolved so that if
the RuntimeDyld client moves the object, it can update the address and any
relocations to that object will be updated.
For our trival object file load/run test harness (llvm-rtdyld), this enables
relocations between functions located in the same object module. It should
be trivially extendable to load multiple objects with mutual references.
As a simple example, the following now works (running on x86_64 Darwin 10.6):
$ cat t.c
int bar() {
return 65;
}
int main() {
return bar();
}
$ clang t.c -fno-asynchronous-unwind-tables -o t.o -c
$ otool -vt t.o
t.o:
(__TEXT,__text) section
_bar:
0000000000000000 pushq %rbp
0000000000000001 movq %rsp,%rbp
0000000000000004 movl $0x00000041,%eax
0000000000000009 popq %rbp
000000000000000a ret
000000000000000b nopl 0x00(%rax,%rax)
_main:
0000000000000010 pushq %rbp
0000000000000011 movq %rsp,%rbp
0000000000000014 subq $0x10,%rsp
0000000000000018 movl $0x00000000,0xfc(%rbp)
000000000000001f callq 0x00000024
0000000000000024 addq $0x10,%rsp
0000000000000028 popq %rbp
0000000000000029 ret
$ llvm-rtdyld t.o -debug-only=dyld ; echo $?
Function sym: '_bar' @ 0
Function sym: '_main' @ 16
Extracting function: _bar from [0, 15]
allocated to 0x100153000
Extracting function: _main from [16, 41]
allocated to 0x100154000
Relocation at '_main' + 16 from '_bar(Word1: 0x2d000000)
Resolving relocation at '_main' + 16 (0x100154010) from '_bar (0x100153000)(pcrel, type: 2, Size: 4).
loaded '_main' at: 0x100154000
65
$
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