discussions with Andy. Fundamentally, the previous algorithm is both
counter productive on several fronts and prioritizing things which
aren't necessarily the most important: static branch prediction.
The new algorithm uses the existing loop CFG structure information to
walk through the CFG itself to layout blocks. It coalesces adjacent
blocks within the loop where the CFG allows based on the most likely
path taken. Finally, it topologically orders the block chains that have
been formed. This allows it to choose a (mostly) topologically valid
ordering which still priorizes fallthrough within the structural
constraints.
As a final twist in the algorithm, it does violate the CFG when it
discovers a "hot" edge, that is an edge that is more than 4x hotter than
the competing edges in the CFG. These are forcibly merged into
a fallthrough chain.
Future transformations that need te be added are rotation of loop exit
conditions to be fallthrough, and better isolation of cold block chains.
I'm also planning on adding statistics to model how well the algorithm
does at laying out blocks based on the probabilities it receives.
The old tests mostly still pass, and I have some new tests to add, but
the nested loops are still behaving very strangely. This almost seems
like working-as-intended as it rotated the exit branch to be
fallthrough, but I'm not convinced this is actually the best layout. It
is well supported by the probabilities for loops we currently get, but
those are pretty broken for nested loops, so this may change later.
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SHL inserts zeros from the right, thus even when the original
sign_extend_inreg value was of 1-bit, we need to sra.
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ZExtPromotedInteger and SExtPromotedInteger based on the operation we legalize.
SetCC return type needs to be legalized via PromoteTargetBoolean.
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it's a bit more plausible to use this instead of CodePlacementOpt. The
code for this was shamelessly stolen from CodePlacementOpt, and then
trimmed down a bit. There doesn't seem to be much utility in returning
true/false from this pass as we may or may not have rewritten all of the
blocks. Also, the statistic of counting how many loops were aligned
doesn't seem terribly important so I removed it. If folks would like it
to be included, I'm happy to add it back.
This was probably the most egregious of the missing features, and now
I'm going to start gathering some performance numbers and looking at
specific loop structures that have different layout between the two.
Test is updated to include both basic loop alignment and nested loop
alignment.
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canonical example I used when developing it, and is one of the primary
motivating real-world use cases for __builtin_expect (when burried under
a macro).
I'm working on more test cases here, but I'm trying to make sure both
that the pass is doing the right thing with the test cases and that they
aren't too brittle to changes elsewhere in the code generation pipeline.
Feedback and/or suggestions on how to test this are very welcome.
Especially feedback on whether testing the block comments is a good
strategy; I couldn't find any good examples to steal from but all the
other ideas I had were a lot uglier or more fragile.
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When checking the availability of instructions using the TLI, a 'promoted'
instruction IS available. It means that the value is bitcasted to another type
for which there is an operation. The correct check for the availablity of an
instruction is to check if it should be expanded.
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On spec/gcc, this caused a codesize improvement of ~1.9% for ARM mode and ~4.9% for Thumb(2) mode. This is
codesize including literal pools.
The pools themselves doubled in size for ARM mode and quintupled for Thumb mode, leaving suggestion that there
is still perhaps redundancy in LLVM's use of constant pools that could be decreased by sharing entries.
Fixes PR11087.
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svn r139159 caused SelectionDAG::getConstant() to promote BUILD_VECTOR operands
with illegal types, even before type legalization. For this testcase, that led
to one BUILD_VECTOR with i16 operands and another with promoted i32 operands,
which triggered the assertion.
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.file filenumber "directory" "filename"
This removes one join+split of the directory+filename in MC internals. Because
bitcode files have independent fields for directory and filenames in debug info,
this patch may change the .o files written by existing .bc files.
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The decision was to pack the bits. Currently no codegen supports this.
Currently, all of the bits in the vector are saved into the same address
in memory.
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When spilling around an instruction with a dead def, remember to add a
value number for the def.
The missing value number wouldn't normally create problems since there
would be an incoming live range as well. However, due to another bug
we could spill a dead V_SET0 instruction which doesn't read any values.
The missing value number caused an empty live range to be created which
is dangerous since it doesn't interfere with anything.
This fixes part of PR11125.
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release the stack segment and reset the stack pointer. Place the code in its own
MBB to make the verifier happy.
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Now that MI->getRegClassConstraint() can also handle inline assembly,
don't bail when recomputing the register class of a virtual register
used by inline asm.
This fixes PR11078.
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our current machine instruction defines a register with the same register class
as what's being replaced. This showed up in the SPEC 403.gcc benchmark, where it
would ICE because a tail call was expecting one register class but was given
another. (The machine instruction verifier catches this situation.)
<rdar://problem/10270968>
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When widening a copy, we are reading a larger register that may not be
live. Use an <undef> flag to tell the register scavenger and machine
code verifier that we know the value isn't defined.
We now widen:
%S6<def> = COPY %S4<kill>, %D3<imp-def>
into:
%D3<def> = VMOVD %D2<undef>, pred:14, pred:%noreg, %S4<imp-use,kill>
This also keeps the <kill> flag on %S4 so we don't inadvertently kill a
live value in %S5.
Finally, ensure that ARMBaseInstrInfo::setExecutionDomain() preserves
the <undef> flag when converting VMOVD to VORR.
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file. Since it should only be used when necessary propagate it through
the backend code generation and tweak testcases accordingly.
This helps with code like in clang's test/CodeGen/debug-info-line.c where
we have multiple #line directives within a single lexical block and want
to generate only a single block that contains each file change.
Part of rdar://10246360
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For example, MachineLICM should not hoist a load that is not guaranteed to be executed.
Radar 10254254.
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For example, MachineLICM should not hoist a load that is not guaranteed to be executed.
Radar 10254254.
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ARMII::AddrModeT1_s, we need to take into account that if the frame register is
ARM::SP, then the number of bits is 8. If it's not ARM::SP, then the number of
bits is 5.
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In 64-bit mode, sub_8bit_hi sub-registers can only be used by NOREX
instructions. The COPY created from the EXTRACT_SUBREG DAG node cannot
target all GR8 registers, only those in GR8_NOREX.
TO enforce this, we ensure that all instructions using the
EXTRACT_SUBREG are GR8_NOREX constrained.
This fixes PR11088.
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merging an lsl #2 that has multiple uses on A9. This shift is free, so there is
no problem merging it in multiple places. Other unprofitable shifts will not be
merged.
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and the alignment is 0 (i.e., it's defined globally in one file and declared in
another file) it could get an alignment which is larger than the ABI allows for
that type, resulting in aligned moves being used for unaligned loads.
For instance, in file A.c:
struct S s;
In file B.c:
struct {
// something long
};
extern S s;
void foo() {
struct S p = s;
// ...
}
this copy is a 'memcpy' which is turned into a series of 'movaps' instructions
on X86. But this is wrong, because 'struct S' has alignment of 4, not 16.
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Rewriting the entire loop nest now requires -enable-lsr-nested.
See PR11035 for some performance data.
A few unit tests specifically test nested LSR, and are now under a flag.
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Lay some groundwork for converting to MC-based asm printer. This is the first
of probably many patches to bring the back-end back up-to-date with all of the
recent MC changes.
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This also enables domain swizzling for AVX code which required a few
trivial test changes.
The pass will be moved to lib/CodeGen shortly.
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