Some of these maps may merge in the future, but for now it's convenient to have
a utility function for them.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119587 91177308-0d34-0410-b5e6-96231b3b80d8
memoize the results. This improves compile time in code which highly complex
expressions which get queried many times.
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needs to be checked that this won't break LCSSA form.
Change the existing checking method to a more direct one:
rather than seeing if all predecessors belong to the loop,
check that the replacing value is either not in any loop or
is in a loop that contains the phi node.
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instructions out of InstCombine and into InstructionSimplify. While
there, introduce an m_AllOnes pattern to simplify matching with integers
and vectors with all bits equal to one.
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phi node itself if it occurs in an unreachable basic block. Protect
against this. Hopefully this will fix some more buildbots.
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simplified to itself (this can only happen in unreachable blocks).
Change it to return null instead. Hopefully this will fix some
buildbot failures.
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class, uses DominatorTree which is an analysis. This change moves all of
the tricky hasConstantValue logic to SimplifyInstruction, and replaces it
with a very simple literal implementation. I already taught users of
hasConstantValue that need tricky stuff to use SimplifyInstruction instead.
I didn't update InlineFunction because the IR looks like it might be in a
funky state at the point it calls hasConstantValue, which makes calling
SimplifyInstruction dangerous since it can in theory do a lot of tricky
reasoning. This may be a pessimization, for example in the case where
all phi node operands are either undef or a fixed constant.
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over a phi node by applying it to each operand may be wrong if the
operation and the phi node are mutually interdependent (the testcase
has a simple example of this). So only do this transform if it would
be correct to perform the operation in each predecessor of the block
containing the phi, i.e. if the other operands all dominate the phi.
This should fix the FFMPEG snow.c regression reported by İsmail Dönmez.
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offload the work to hasConstantValue rather than do something more
complicated (such handling mutually recursive phis) because (1) it is
not clear it is worth it; and (2) if it is worth it, maybe such logic
would be better placed in hasConstantValue. Adjust some GVN tests
which are now cleaned up much further (eg: all phi nodes are removed).
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operands are the phi node itself or undef, then return undef.
This logic already existed at a higher level so in practice it
shouldn't make the slightest difference. Note that this code
could be replaced by a call to PN->hasConstantValue(). However
since we bail out the moment we see a non-constant operand, it
is more efficient to have a specialized version of that logic.
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references. For example, this allows gvn to eliminate the load in
this example:
void foo(int n, int* p, int *q) {
p[0] = 0;
p[1] = 1;
if (n) {
*q = p[0];
}
}
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nodes can be used in loops, this could result in infinite looping
if there is no recursion limit, so add such a limit. It is also
used for the SelectInst case because in theory there could be an
infinite loop there too if the basic block is unreachable.
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The simplifications performed here never create new instructions, they
only return existing instructions (or a constant), and so are always a
win. In theory they should transform (for example)
%z = and i32 %x, %y
%s = select i1 %cond, i32 %y, i32 %z
%r = and i32 %x, %s
into
%r = and i32 %x, y
but in practice they get into a fight with instcombine, and lose.
Unfortunately instcombine does a poor job in this case. Nonetheless
I'm committing this transform to make it easier to discuss what to
do to make peace with instcombine.
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to optionally look for constant or local (alloca) memory.
Teach BasicAliasAnalysis::pointsToConstantMemory to look through Select
and Phi nodes, and to support looking for local memory.
Remove FunctionAttrs' PointsToLocalOrConstantMemory function, now that
AliasAnalysis knows all the tricks that it knew.
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of a select instruction, see if doing the compare with the
true and false values of the select gives the same result.
If so, that can be used as the value of the comparison.
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