Commit Graph

75 Commits

Author SHA1 Message Date
Jakob Stoklund Olesen d0d7860f40 Pass an explicit operand number to addLiveIns.
Not all instructions define a virtual register in their first operand.
Specifically, INLINEASM has a different format.

<rdar://problem/12472811>

llvm-svn: 165721
2012-10-11 16:46:07 +00:00
Jakob Stoklund Olesen 9d1173a86e Don't crash on extra evil irreducible control flow.
When the CFG contains a loop with multiple entry blocks, the traces
computed by MachineTraceMetrics don't always have the same nice
properties. Loop back-edges are normally excluded from traces, but
MachineLoopInfo doesn't recognize loops with multiple entry blocks, so
those back-edges may be included.

Avoid asserting when that happens by adding an isEarlierInSameTrace()
function that accurately determines if a dominating block is part of the
same trace AND is above the currrent block in the trace.

llvm-svn: 165434
2012-10-08 22:06:44 +00:00
Jakob Stoklund Olesen 8982222917 Switch MachineTraceMetrics to the new TargetSchedModel interface.
llvm-svn: 165235
2012-10-04 17:30:40 +00:00
Jakob Stoklund Olesen a0042acd3b Give MachineTraceMetrics its own debug tag.
llvm-svn: 161712
2012-08-10 22:27:29 +00:00
Jakob Stoklund Olesen 3484420927 Add more trace query functions.
Trace::getResourceLength() computes the number of cycles required to
execute the trace when ignoring data dependencies. The number can be
compared to the critical path to estimate the trace ILP.

Trace::getPHIDepth() computes the data dependency depth of a PHI in a
trace successor that isn't necessarily part of the trace.

llvm-svn: 161711
2012-08-10 22:27:27 +00:00
Jakob Stoklund Olesen 0954d4199a Include loop-carried dependencies when computing instr heights.
When a trace ends with a back-edge, include PHIs in the loop header in
the height computations. This makes the critical path through a loop
more accurate by including the latencies of the last instructions in the
loop.

llvm-svn: 161688
2012-08-10 20:11:38 +00:00
Jakob Stoklund Olesen bf1ac4bdc3 Deal with irreducible control flow when building traces.
We filter out MachineLoop back-edges during the trace-building PO
traversals, but it is possible to have CFG cycles that aren't natural
loops, and MachineLoopInfo doesn't include such cycles.

Use a standard visited set to detect such CFG cycles, and completely
ignore them when picking traces.

llvm-svn: 161532
2012-08-08 22:12:01 +00:00
Jakob Stoklund Olesen 296448b293 Fix a couple of typos.
llvm-svn: 161437
2012-08-07 18:32:57 +00:00
Jakob Stoklund Olesen 75d9d5159e Add trace accessor methods, implement primitive if-conversion heuristic.
Compare the critical paths of the two traces through an if-conversion
candidate. If the difference is larger than the branch brediction
penalty, reject the if-conversion. If would never pay.

llvm-svn: 161433
2012-08-07 18:02:19 +00:00
Jakob Stoklund Olesen 5d30630e22 Compute the critical path length through a trace.
Whenever both instruction depths and instruction heights are known in a
block, it is possible to compute the length of the critical path as
max(depth+height) over the instructions in the block.

The stored live-in lists make it possible to accurately compute the
length of a critical path that bypasses the current (small) block.

llvm-svn: 161197
2012-08-02 18:45:54 +00:00
Jakob Stoklund Olesen 2db6b65330 Compute instruction heights through a trace.
The height on an instruction is the minimum number of cycles from the
instruction is issued to the end of the trace. Heights are computed for
all instructions in and below the trace center block.

The method for computing heights is different from the depth
computation. As we visit instructions in the trace bottom-up, heights of
used instructions are pushed upwards. This way, we avoid scanning long
use lists, looking for uses in the current trace.

At each basic block boundary, a list of live-in registers and their
minimum heights is saved in the trace block info. These live-in lists
are used when restarting depth computations on a trace that
converges with an already computed trace. They will also be used to
accurately compute the critical path length.

llvm-svn: 161138
2012-08-01 22:36:00 +00:00
Jakob Stoklund Olesen 5e19d35e9a Add DataDep constructors. Explicitly check SSA form.
llvm-svn: 161115
2012-08-01 16:02:59 +00:00
Jakob Stoklund Olesen 059e647c6d Compute instruction depths through the current trace.
Assuming infinite issue width, compute the earliest each instruction in
the trace can issue, when considering the latency of data dependencies.
The issue cycle is record as a 'depth' from the beginning of the trace.

This is half the computation required to find the length of the critical
path through the trace. Heights are next.

llvm-svn: 161074
2012-07-31 20:44:38 +00:00
Jakob Stoklund Olesen 1dfb101835 Rename CT -> MTM. MachineTraceMetrics is abbreviated MTM.
llvm-svn: 161072
2012-07-31 20:25:13 +00:00
Jakob Stoklund Olesen 68c2cd059e Avoid looking at stale data in verifyAnalysis().
llvm-svn: 161004
2012-07-30 23:15:12 +00:00
Jakob Stoklund Olesen c14cf57ba9 Allow traces to enter nested loops.
This lets traces include the final iteration of a nested loop above the
center block, and the first iteration of a nested loop below the center
block.

We still don't allow traces to contain backedges, and traces are
truncated where they would leave a loop, as seen from the center block.

llvm-svn: 161003
2012-07-30 23:15:10 +00:00
Jakob Stoklund Olesen f308c128ea Assert that all trace candidate blocks have been visited by the PO.
When computing a trace, all the candidates for pred/succ must have been
visited. Filter out back-edges first, though. The PO traversal ignores
them.

Thanks to Andy for spotting this in review.

llvm-svn: 160995
2012-07-30 21:10:27 +00:00
Jakob Stoklund Olesen a12a7d5f74 Hook into PassManager's analysis verification.
By overriding Pass::verifyAnalysis(), the pass contents will be verified
by the pass manager.

llvm-svn: 160994
2012-07-30 20:57:50 +00:00
Jakob Stoklund Olesen 7361846f32 Add MachineInstr::isTransient().
This is a cleaned up version of the isFree() function in
MachineTraceMetrics.cpp.

Transient instructions are very unlikely to produce any code in the
final output. Either because they get eliminated by RegisterCoalescing,
or because they are pseudo-instructions like labels and debug values.

llvm-svn: 160977
2012-07-30 18:34:14 +00:00
Jakob Stoklund Olesen 3df6c46fdd Add MachineTraceMetrics::verify().
This function verifies the consistency of cached data in the
MachineTraceMetrics analysis.

llvm-svn: 160976
2012-07-30 18:34:11 +00:00
Jakob Stoklund Olesen eb488fe165 Verify that the CFG hasn't changed during invalidate().
The MachineTraceMetrics analysis must be invalidated before modifying
the CFG. This will catch some of the violations of that rule.

llvm-svn: 160969
2012-07-30 17:36:49 +00:00
Jakob Stoklund Olesen 0563369755 Add more debug output to MachineTraceMetrics.
llvm-svn: 160905
2012-07-27 23:58:38 +00:00
Jakob Stoklund Olesen 1152202cc2 Keep track of the head and tail of the trace through each block.
This makes it possible to quickly detect blocks that are outside the
trace.

llvm-svn: 160904
2012-07-27 23:58:36 +00:00
Jakob Stoklund Olesen 35400b1dda Use an otherwise unused variable.
llvm-svn: 160798
2012-07-26 19:42:56 +00:00
Jakob Stoklund Olesen f9029fef2a Start scaffolding for a MachineTraceMetrics analysis pass.
This is still a work in progress.

Out-of-order CPUs usually execute instructions from multiple basic
blocks simultaneously, so it is necessary to look at longer traces when
estimating the performance effects of code transformations.

The MachineTraceMetrics analysis will pick a typical trace through a
given basic block and provide performance metrics for the trace. Metrics
will include:

- Instruction count through the trace.
- Issue count per functional unit.
- Critical path length, and per-instruction 'slack'.

These metrics can be used to determine the performance limiting factor
when executing the trace, and how it will be affected by a code
transformation.

Initially, this will be used by the early if-conversion pass.

llvm-svn: 160796
2012-07-26 18:38:11 +00:00