When updating the worklist for InstCombine, the Add/AddUsersToWorklist
functions may access the instruction(s) being added, for debug output for
example. If the instructions aren't yet added to the basic block, this
can result in a crash. Finish the instruction transformation before
adjusting the worklist instead.
rdar://10238555
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branch "br i1 %x, label %if_true, label %if_false" then it replaces
"%x" with "true" in places only reachable via the %if_true arm, and
with "false" in places only reachable via the %if_false arm. Except
that actually it doesn't: if value numbering shows that %y is equal
to %x then, yes, %y will be turned into true/false in this way, but
any occurrences of %x itself are not transformed. Fix this. What's
more, it's often the case that %x is an equality comparison such as
"%x = icmp eq %A, 0", in which case every occurrence of %A that is
only reachable via the %if_true arm can be replaced with 0. Implement
this and a few other variations on this theme. This reduces the number
of lines of LLVM IR in "GCC as one big file" by 0.2%. It has a bigger
impact on Ada code, typically reducing the number of lines of bitcode
by around 0.4% by removing repeated compiler generated checks. Passes
the LLVM nightly testsuite and the Ada ACATS testsuite.
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it's OK for the false/true destination to have multiple
predecessors as long as the extra ones are dominated by
the branch destination.
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This handles the case in which LSR rewrites an IV user that is a phi and
splits critical edges originating from a switch.
Fixes <rdar://problem/6453893> LSR is not splitting edges "nicely"
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We want heuristics to be based on accurate data, but more importantly
we don't want llvm to behave randomly. A benign trunc inserted by an
upstream pass should not cause a wild swings in optimization
level. See PR11034. It's a general problem with threshold-based
heuristics, but we can make it less bad.
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catch or repeated filter clauses. Teach instcombine a bunch
of tricks for simplifying landingpad clauses. Currently the
code only recognizes the GNU C++ and Ada personality functions,
but that doesn't stop it doing a bunch of "generic" transforms
which are hopefully fine for any real-world personality function.
If these "generic" transforms turn out not to be generic, they
can always be conditioned on the personality function. Probably
someone should add the ObjC++ personality function. I didn't as
I don't know anything about it.
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objc_retainBlock call is potentially responsible for copying
the block to the heap to extend its lifetime. rdar://10209613.
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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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Disabling aggressive LSR saves compilation time, and with the new
indvars behavior usually improves performance.
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The minor bug heuristic was noticed by inspection. I added the
isLoser/isValid helpers because they will become more
important with subsequent checkins.
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No test case. Noticed by inspection and I doubt it ever affects the
outcome of the overall heuristic, let alone final codegen.
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The landing pad must accompany the invoke when it's extracted. However, if it
does, then the loop isn't properly extracted. I.e., the resulting extraction has
a loop in it. The extracted function is then extracted, etc. resulting in an
infinite loop.
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extract its associated landing pad block as well. However, that landing pad
block may have more than one predecessor. So split the landing pad block so that
individual landing pads have only one predecessor.
This type of transformation may produce a false positive with bugpoint.
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extract the landing pad block. Otherwise, there will be a situation where the
invoke's unwind edge lands on a non-landing pad.
We also forbid the user from extracting the landing pad block by itself. Again,
this is not a valid transformation.
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No tests; these changes aren't really interesting in the sense that the logic is the same for volatile and atomic.
I believe this completes all of the changes necessary for the optimizer to handle loads and stores correctly. I'm going to try and come up with some additional testing, though.
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better.
Don't immediately give up when an add operation can't be trivially
sign/zero-extended within a loop. If it has NSW/NUW flags, generate a
new expression with sign extended (non-recurrent) operand. As before,
if SCEV says that all sign extends are loop invariant, then we can
widen the operation.
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init.trampoline and adjust.trampoline intrinsics, into two intrinsics
like in GCC. While having one combined intrinsic is tempting, it is
not natural because typically the trampoline initialization needs to
be done in one function, and the result of adjust trampoline is needed
in a different (nested) function. To get around this llvm-gcc hacks the
nested function lowering code to insert an additional parent variable
holding the adjust.trampoline result that can be accessed from the child
function. Dragonegg doesn't have the luxury of tweaking GCC code, so it
stored the result of adjust.trampoline in the memory GCC set aside for
the trampoline itself (this is always available in the child function),
and set up some new memory (using an alloca) to hold the trampoline.
Unfortunately this breaks Go which allocates trampoline memory on the
heap and wants to use it even after the parent has exited (!). Rather
than doing even more hacks to get Go working, it seemed best to just use
two intrinsics like in GCC. Patch mostly by Sanjoy Das.
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This changes loop unrolling to use the same mechanism for trip count
computation as indvars. This is a stronger check that tends to unroll
more loops. A very common side-effect is that many single iteration
loops will be removed sooner. The real goal was simply to remove
dependence on canonical IVs.
x86 is break even.
ARM performance changes to expect (+ is good):
External/SPEC/CFP2000/183.equake/183.equake +13%
SingleSource/Benchmarks/Dhrystone/fldry +21%
MultiSource/Applications/spiff/spiff +3%
SingleSource/Benchmarks/Stanford/Puzzle -14%
The Puzzle regression is actually an improvement in loop optimization
that defeats GVN: rdar://problem/10065079.
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The landingpad instruction is required in the landing pad block. Because we're
not deleting terminating instructions, the invoke may still jump to here (see
Transforms/SCCP/2004-11-16-DeadInvoke.ll). Remove all uses of the landingpad
instruction, but keep it around until code-gen can remove the basic block.
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ssa, so it has to be run really early in the pipeline. Any replacement
should probably use the SSAUpdater.
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Optimize chained bitcasts of the form A->B->A.
Undo r138722 and change isEliminableCastPair to allow this case.
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In theory this could be extended to other instructions, eg. division by zero, but it's likely that it will "miscompile" some code because people depend on div by zero not trapping. NULL pointer dereference usually leads to a crash so we should be on the safe side.
This shrinks the size of a Release clang by 16k on x86_64.
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known-incremented level, because the two concepts can be used
to prove the saftey of a retain+release removal in different
ways.
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We have to be careful when splitting the landing pad block, because the
landingpad instruction is required to remain as the first non-PHI of an invoke's
unwind edge. To retain this, we split the block into two blocks, moving the
predecessors within the loop to one block and the remaining predecessors to the
other. The landingpad instruction is cloned into the new blocks.
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SplitLandingPadPredecessors is similar to SplitBlockPredecessors in that it
splits the current block and attaches a set of predecessors to the new basic
block. However, it differs from SplitBlockPredecessors in that it's specifically
designed to handle landing pad blocks.
Two new basic blocks are created: one that is has the vector of predecessors as
its predecessors and one that has the remaining predecessors as its
predecessors. Those two new blocks then receive a cloned copy of the landingpad
instruction from the original block. The landingpad instructions are joined in a
PHI, etc. Like SplitBlockPredecessors, it updates the LLVM IR, AliasAnalysis,
DominatorTree, DominanceFrontier, LoopInfo, and LCCSA analyses.
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