#1 is to unconditionally strip constantpointerrefs out of
instruction operands where they are absolutely pointless and inhibit
optimization. GRRR!
#2 is to implement InstCombine/getelementptr_const.ll
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With this fix we now successfully extract all 149 loops from 256.bzip2 without
crashing or miscompiling the program!
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1. Names were not put on the new arguments created (ok, this just helps sanity :)
2. Fix outgoing pointer values
3. Do not insert stores for values that had not been computed
4. Fix some wierd problems with the outset calculation
This fixes CodeExtractor/2004-03-14-DominanceProblem.ll, making the extractor
work on at least one simple case!
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as it is making effectively arbitrary modifications to the CFG and we don't
have a domset/domfrontier implementations that can handle the dynamic updates.
Instead of having a bunch of code that doesn't actually work in practice,
just demote any potentially tricky values to the stack (causing the problem
to go away entirely). Later invocations of mem2reg will rebuild SSA for us.
This fixes all of the major performance regressions with tail duplication
from LLVM 1.1. For example, this loop:
---
int popcount(int x) {
int result = 0;
while (x != 0) {
result = result + (x & 0x1);
x = x >> 1;
}
return result;
}
---
Used to be compiled into:
int %popcount(int %X) {
entry:
br label %loopentry
loopentry: ; preds = %entry, %no_exit
%x.0 = phi int [ %X, %entry ], [ %tmp.9, %no_exit ] ; <int> [#uses=3]
%result.1.0 = phi int [ 0, %entry ], [ %tmp.6, %no_exit ] ; <int> [#uses=2]
%tmp.1 = seteq int %x.0, 0 ; <bool> [#uses=1]
br bool %tmp.1, label %loopexit, label %no_exit
no_exit: ; preds = %loopentry
%tmp.4 = and int %x.0, 1 ; <int> [#uses=1]
%tmp.6 = add int %tmp.4, %result.1.0 ; <int> [#uses=1]
%tmp.9 = shr int %x.0, ubyte 1 ; <int> [#uses=1]
br label %loopentry
loopexit: ; preds = %loopentry
ret int %result.1.0
}
And is now compiled into:
int %popcount(int %X) {
entry:
br label %no_exit
no_exit: ; preds = %entry, %no_exit
%x.0.0 = phi int [ %X, %entry ], [ %tmp.9, %no_exit ] ; <int> [#uses=2]
%result.1.0.0 = phi int [ 0, %entry ], [ %tmp.6, %no_exit ] ; <int> [#uses=1]
%tmp.4 = and int %x.0.0, 1 ; <int> [#uses=1]
%tmp.6 = add int %tmp.4, %result.1.0.0 ; <int> [#uses=2]
%tmp.9 = shr int %x.0.0, ubyte 1 ; <int> [#uses=2]
%tmp.1 = seteq int %tmp.9, 0 ; <bool> [#uses=1]
br bool %tmp.1, label %loopexit, label %no_exit
loopexit: ; preds = %no_exit
ret int %tmp.6
}
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time from 615s to 1.49s on a large testcase that has a gigantic switch statement
that all of the blocks in the function go to (an intepreter).
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Simplify the input/output finder. All elements of a basic block are
instructions. Any used arguments are also inputs. An instruction can only
be used by another instruction.
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extracted, and a function that contained a single top-level loop never had
the loop extracted, regardless of how much non-loop code there was.
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* Don't insert a branch to the switch instruction after the call, just
make it a single block.
* Insert the new alloca instructions in the entry block of the original
function instead of having them execute dynamically
* Don't make the default edge of the switch instruction go back to the switch.
The loop extractor shouldn't create new loops!
* Give meaningful names to the alloca slots and the reload instructions
* Some minor code simplifications
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This also implements a two minor improvements:
* Don't insert live-out stores IN the region, insert them on the code path
that exits the region
* If the region is exited to the same block from multiple paths, share the
switch statement entry, live-out store code, and the basic block.
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a member of the class. While we're at it, turn the collection into a set
instead of a vector to improve efficiency and make queries simpler.
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Require 'simplified' loops, not just raw natural loops. This fixes
CodeExtractor/2004-03-13-LoopExtractorCrash.ll
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loop information won't see it, and we could have unreachable blocks pointing to
the non-header node of blocks in a natural loop. This isn't tidy, so have the
loopsimplify pass clean it up.
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Fix InstCombine/2004-03-13-InstCombineInfLoop.ll which caused an infinite
loop compiling (I think) povray.
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* Be a lot more accurate about what the effects will be when inlining a call
to a function when an argument is an alloca.
* Dramatically reduce the penalty for inlining a call in a large function.
This heuristic made it almost impossible to inline a function into a large
function, no matter how small the callee is.
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On the testcase from GCC PR12440, which has a LOT of loops (1392 of which require
preheaders to be inserted), this speeds up the loopsimplify pass from 1.931s to
0.1875s. The loop in question goes from 1.65s -> 0.0097s, which isn't bad. All of
these times are a debug build.
This adds a dependency on DominatorTree analysis that was not there before, but
we always had dominatortree available anyway, because LICM requires both loop
simplify and DT, so this doesn't add any extra analysis in practice.
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This allows pointers to aggregate objects, whose elements are only read, to
be promoted and passed in by element instead of by reference. This can
enable a LOT of subsequent optimizations in the caller function.
It's worth pointing out that this stuff happens a LOT of C++ programs, because
objects in templates are generally passed around by reference. When these
templates are instantiated on small aggregate or scalar types, however, it is
more efficient to pass them in by value than by reference.
This transformation triggers most on C++ codes (e.g. 334 times on eon), but
does happen on C codes as well. For example, on mesa it triggers 72 times,
and on gcc it triggers 35 times. this is amazingly good considering that
we are using 'basicaa' so far.
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Note that this is a band-aid put over a band-aid. This just undisables
tail duplication in on very specific case that it seems to work in.
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function, as long as the loop isn't the only one in that function. This should
help debugging passes easier with BugPoint.
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This is a really minor thing, but might help out the 'switch statement induction'
code in simplifycfg.
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assume that if they don't intend to write to a global variable, that they
would mark it as constant. However, there are people that don't understand
that the compiler can do nice things for them if they give it the information
it needs.
This pass looks for blatently obvious globals that are only ever read from.
Though it uses a trivially simple "alias analysis" of sorts, it is still able
to do amazing things to important benchmarks. 253.perlbmk, for example,
contains several ***GIANT*** function pointer tables that are not marked
constant and should be. Marking them constant allows the optimizer to turn
a whole bunch of indirect calls into direct calls. Note that only a link-time
optimizer can do this transformation, but perlbmk does have several strings
and other minor globals that can be marked constant by this pass when run
from GCCAS.
176.gcc has a ton of strings and large tables that are marked constant, both
at compile time (38 of them) and at link time (48 more). Other benchmarks
give similar results, though it seems like big ones have disproportionally
more than small ones.
This pass is extremely quick and does good things. I'm going to enable it
in gccas & gccld. Not bad for 50 SLOC.
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This case occurs many times in various benchmarks, especially when combined
with the previous patch. This allows it to get stuff like:
if (X == 4 || X == 3)
if (X == 5 || X == 8)
and
switch (X) {
case 4: case 5: case 6:
if (X == 4 || X == 5)
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allowed in invoke instructions. Thus, if we are inlining a call to an intrinsic
function into an invoke site, we don't need to turn the call into an invoke!
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more of a testcase for profiling information than anything that should reasonably
be used, but it's a starting point. When I have more time I will whip this into
better shape.
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Having a proper 'select' instruction would allow the elimination of a lot
of the special case cruft in this patch, but we don't have one yet.
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passed into main, make sure they use the return value of the init call
instead of the one passed in.
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This causes the JIT, or LLC'd program to print out a nice message, explaining
WHY the program aborted.
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The problem is that the dominator update code didn't "realize" that it's
possible for the newly inserted basic block to dominate anything. Because
it IS possible, stuff was getting updated wrong.
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1. Don't scan to the end of alloca instructions in the caller function to
insert inlined allocas, just insert at the top. This saves a lot of
time inlining into functions with a lot of allocas.
2. Use splice to move the alloca instructions over, instead of remove/insert.
This allows us to transfer a block at a time, and eliminates a bunch of
silly symbol table manipulations.
This speeds up the inliner on the testcase in PR209 from 1.73s -> 1.04s (67%)
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and that basic block ends with a return instruction. In this case, we can just splice
the cloned "body" of the function directly into the source basic block, avoiding a lot
of rearrangement and splitBasicBlock's linear scan over the split block. This speeds up
the inliner on the testcase in PR209 from 2.3s to 1.7s, a 35% reduction.
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before we delete the original call site, allowing slight simplifications of
code, but nothing exciting.
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process. The only optimization we did so far is to avoid creating a
PHI node, then immediately destroying it in the common case where the
callee has one return statement. Instead, we just don't create the return
value. This has no noticable performance impact, but paves the way for
future improvements.
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to add the cloned block to. This allows the block to be added to the function
immediately, and all of the instructions to be immediately added to the function
symbol table, which speeds up the inliner from 3.7 -> 3.38s on the PR209.
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process them all as a group. This speeds up SRoA/mem2reg from 28.46s to
0.62s on the testcase from PR209.
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