Commit Graph

13 Commits

Author SHA1 Message Date
Chandler Carruth
73527d30cd Fix a stunning oversight in the inline cost analysis. It was never
propagating one of the values it simplified to a constant across
a myriad of instructions. Notably, ptrtoint instructions when we had
a constant pointer (say, 0) didn't propagate that, blocking a massive
number of down-stream optimizations.

This was uncovered when investigating why we fail to inline and delete
the boilerplate in:

  void f() {
    std::vector<int> v;
    v.push_back(1);
  }

It turns out most of the efforts I've made thus far to improve the
analysis weren't making it far purely because of this. After this is
fixed, the store-to-load forwarding patch enables LLVM to optimize the
above to an empty function. We still can't nuke a second push_back, but
for different reasons.

There is a very real chance this will cause somewhat noticable changes
in inlining behavior, so please let me know if you see regressions (or
improvements!) because of this patch.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171196 91177308-0d34-0410-b5e6-96231b3b80d8
2012-12-28 14:43:42 +00:00
Chandler Carruth
ba94204e94 Teach the inline cost analysis about calls that can be simplified and
how to propagate constants through insert and extract value
instructions.

With the recent improvements to instsimplify, this allows inline cost
analysis to constant fold through intrinsic functions, including notably
the with.overflow intrinsic math routines which often show up inside of
STL abstractions. This is yet another piece in the puzzle of breaking
down the code for:

  void f() {
    std::vector<int> v;
    v.push_back(1);
  }

But it still isn't enough. There are a pile of bugs in inline cost still
blocking this.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171195 91177308-0d34-0410-b5e6-96231b3b80d8
2012-12-28 14:23:32 +00:00
Chandler Carruth
961e1acfb2 Fix PR13412, a nasty miscompile due to the interleaved
instsimplify+inline strategy.

The crux of the problem is that instsimplify was reasonably relying on
an invariant that is true within any single function, but is no longer
true mid-inline the way we use it. This invariant is that an argument
pointer != a local (alloca) pointer.

The fix is really light weight though, and allows instsimplify to be
resiliant to these situations: when checking the relation ships to
function arguments, ensure that the argumets come from the same
function. If they come from different functions, then none of these
assumptions hold. All credit to Benjamin Kramer for coming up with this
clever solution to the problem.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161410 91177308-0d34-0410-b5e6-96231b3b80d8
2012-08-07 10:59:59 +00:00
Chandler Carruth
f2286b0152 Initial commit for the rewrite of the inline cost analysis to operate
on a per-callsite walk of the called function's instructions, in
breadth-first order over the potentially reachable set of basic blocks.

This is a major shift in how inline cost analysis works to improve the
accuracy and rationality of inlining decisions. A brief outline of the
algorithm this moves to:

- Build a simplification mapping based on the callsite arguments to the
  function arguments.
- Push the entry block onto a worklist of potentially-live basic blocks.
- Pop the first block off of the *front* of the worklist (for
  breadth-first ordering) and walk its instructions using a custom
  InstVisitor.
- For each instruction's operands, re-map them based on the
  simplification mappings available for the given callsite.
- Compute any simplification possible of the instruction after
  re-mapping, and store that back int othe simplification mapping.
- Compute any bonuses, costs, or other impacts of the instruction on the
  cost metric.
- When the terminator is reached, replace any conditional value in the
  terminator with any simplifications from the mapping we have, and add
  any successors which are not proven to be dead from these
  simplifications to the worklist.
- Pop the next block off of the front of the worklist, and repeat.
- As soon as the cost of inlining exceeds the threshold for the
  callsite, stop analyzing the function in order to bound cost.

The primary goal of this algorithm is to perfectly handle dead code
paths. We do not want any code in trivially dead code paths to impact
inlining decisions. The previous metric was *extremely* flawed here, and
would always subtract the average cost of two successors of
a conditional branch when it was proven to become an unconditional
branch at the callsite. There was no handling of wildly different costs
between the two successors, which would cause inlining when the path
actually taken was too large, and no inlining when the path actually
taken was trivially simple. There was also no handling of the code
*path*, only the immediate successors. These problems vanish completely
now. See the added regression tests for the shiny new features -- we
skip recursive function calls, SROA-killing instructions, and high cost
complex CFG structures when dead at the callsite being analyzed.

Switching to this algorithm required refactoring the inline cost
interface to accept the actual threshold rather than simply returning
a single cost. The resulting interface is pretty bad, and I'm planning
to do lots of interface cleanup after this patch.

Several other refactorings fell out of this, but I've tried to minimize
them for this patch. =/ There is still more cleanup that can be done
here. Please point out anything that you see in review.

I've worked really hard to try to mirror at least the spirit of all of
the previous heuristics in the new model. It's not clear that they are
all correct any more, but I wanted to minimize the change in this single
patch, it's already a bit ridiculous. One heuristic that is *not* yet
mirrored is to allow inlining of functions with a dynamic alloca *if*
the caller has a dynamic alloca. I will add this back, but I think the
most reasonable way requires changes to the inliner itself rather than
just the cost metric, and so I've deferred this for a subsequent patch.
The test case is XFAIL-ed until then.

As mentioned in the review mail, this seems to make Clang run about 1%
to 2% faster in -O0, but makes its binary size grow by just under 4%.
I've looked into the 4% growth, and it can be fixed, but requires
changes to other parts of the inliner.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153812 91177308-0d34-0410-b5e6-96231b3b80d8
2012-03-31 12:42:41 +00:00
Chandler Carruth
6c0b3ac8ea When inlining a function and adding its inner call sites to the
candidate set for subsequent inlining, try to simplify the arguments to
the inner call site now that inlining has been performed.

The goal here is to propagate and fold constants through deeply nested
call chains. Without doing this, we loose the inliner bonus that should
be applied because the arguments don't match the exact pattern the cost
estimator uses.

Reviewed on IRC by Benjamin Kramer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@152556 91177308-0d34-0410-b5e6-96231b3b80d8
2012-03-12 11:19:33 +00:00
Chandler Carruth
747cccf0dc FileCheck-ize this test.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@152554 91177308-0d34-0410-b5e6-96231b3b80d8
2012-03-12 11:19:28 +00:00
Dan Gohman
f2f6ce65b7 Change tests from "opt %s" to "opt < %s" so that opt doesn't see the
input filename so that opt doesn't print the input filename in the
output so that grep lines in the tests don't unintentionally match
strings in the input filename.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@81537 91177308-0d34-0410-b5e6-96231b3b80d8
2009-09-11 18:01:28 +00:00
Dan Gohman
3e054fe9ef Use opt -S instead of piping bitcode output through llvm-dis.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@81257 91177308-0d34-0410-b5e6-96231b3b80d8
2009-09-08 22:34:10 +00:00
Dan Gohman
b1e1e82c54 Change these tests to feed the assembly files to opt directly, instead
of using llvm-as, now that opt supports this.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@81226 91177308-0d34-0410-b5e6-96231b3b80d8
2009-09-08 16:50:01 +00:00
Tanya Lattner
ec9a35a6f9 Remove llvm-upgrade and update test cases.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@47793 91177308-0d34-0410-b5e6-96231b3b80d8
2008-03-01 09:15:35 +00:00
Reid Spencer
2aabd0722d For PR1319:
Upgrade to use new Tcl exec based test harness.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@36062 91177308-0d34-0410-b5e6-96231b3b80d8
2007-04-15 08:30:33 +00:00
Reid Spencer
69ccadd753 Use the llvm-upgrade program to upgrade llvm assembly.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@32115 91177308-0d34-0410-b5e6-96231b3b80d8
2006-12-02 04:23:10 +00:00
Chris Lattner
5ca32a6d6c New testcase: check that the inliner constant folds instructions on the
fly if it can.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@28515 91177308-0d34-0410-b5e6-96231b3b80d8
2006-05-27 01:16:22 +00:00