handle the case when we can infer an input to the xor
from all inputs that agree, instead of going into an
infinite loop. Another part of PR6199
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in JT.
2) When cloning blocks for PHI or xor conditions, use
instsimplify to simplify the code as we go. This allows us to
squish common cases early in JT which opens up opportunities for
subsequent iterations, and allows it to completely simplify the
testcase.
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condition is a xor with a phi node. This eliminates nonsense
like this from 176.gcc in several places:
LBB166_84:
testl %eax, %eax
- setne %al
- xorb %cl, %al
- notb %al
- testb $1, %al
- je LBB166_85
+ je LBB166_69
+ jmp LBB166_85
This is rdar://7391699
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debug intrinsics, and an unconditional branch when possible. This
reuses the TryToSimplifyUncondBranchFromEmptyBlock function split
out of simplifycfg.
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just one level deep. On the testcase we go from getting this:
F1: ; preds = %T2
%F = and i1 true, %cond ; <i1> [#uses=1]
br i1 %F, label %X, label %Y
to a fully threaded:
F1: ; preds = %T2
br label %Y
This changes gets us to the point where we're forming (too many) switch
instructions on doug's strswitch testcase.
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(making pred factoring only happen if threading is guaranteed
to be successful).
This now survives an X86-64 bootstrap of llvm-gcc.
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predicates. This allows us to jump thread things like:
_ZN12StringSwitchI5ColorE4CaseILj7EEERS1_RAT__KcRKS0_.exit119:
%tmp1.i24166 = phi i8 [ 1, %bb5.i117 ], [ %tmp1.i24165, %_Z....exit ], [ %tmp1.i24165, %bb4.i114 ]
%toBoolnot.i87 = icmp eq i8 %tmp1.i24166, 0 ; <i1> [#uses=1]
%tmp4.i90 = icmp eq i32 %tmp2.i, 6 ; <i1> [#uses=1]
%or.cond173 = and i1 %toBoolnot.i87, %tmp4.i90 ; <i1> [#uses=1]
br i1 %or.cond173, label %bb4.i96, label %_ZN12...
Where it is "obvious" that when coming from %bb5.i117 that the 'and' is always
false. This triggers a surprisingly high number of times in the testsuite,
and gets us closer to generating good code for doug's strswitch testcase.
This also make a bunch of other code in jump threading redundant, I'll rip
out in the next patch. This survived an enable-checking llvm-gcc bootstrap.
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When an incoming value for a PHI is updated, we must also updated all other
incoming values for the same BB to match, otherwise we create invalid PHIs.
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done by condprop, but do it in a much more general form. The
basic idea is that we can do a limited form of tail duplication
in the case when we have a branch on a phi. Moving the branch
up in to the predecessor block makes instruction selection
much easier and encourages chained jump threadings.
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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.
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as if they were multiple uses of the same instruction. This interacts
well with the existing loadpre that j-t does to open up many new jump
threads earlier.
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1) have it fold "br undef", which does occur with
surprising frequency as jump threading iterates.
2) teach j-t to delete dead blocks. This removes the successor
edges, reducing the in-edges of other blocks, allowing
recursive simplification.
3) Fold things like:
br COND, BBX, BBY
BBX:
br COND, BBZ, BBW
which also happens because jump threading iterates.
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1. Make it fold blocks separated by an unconditional branch. This enables
jump threading to see a broader scope.
2. Make jump threading able to eliminate locally redundant loads when they
feed the branch condition of a block. This frequently occurs due to
reg2mem running.
3. Make jump threading able to eliminate *partially redundant* loads when
they feed the branch condition of a block. This is common in code with
lots of loads and stores like C++ code and 255.vortex.
This implements thread-loads.ll and rdar://6402033.
Per the fixme's, several pieces of this should be moved into Transforms/Utils.
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DemoteRegToStack doesn't work with MRVs yet, because it relies on the
ability to load/store things.
This fixes PR2285.
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