llvm-svn: 161782

It is still possible to if-convert if the tail block has extra
predecessors, but the tail phis must be rewritten instead of being
removed.

llvm-svn: 161781

Detect when there is not enough available ILP, so if-conversion can't
speculate instructions for free.

Compute the lengthening of the critical path when inserting a select
instruction that depends on the condition as well as both sides of the
if.

Reject conversions that would stretch the critical path by more than
half a mispredict penalty.

llvm-svn: 161713

They identify the PHI predecessors in both diamonds and triangles.

llvm-svn: 161689

llvm-svn: 161513

Thanks, Andy!

llvm-svn: 161507

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

By overriding Pass::verifyAnalysis(), the pass contents will be verified
by the pass manager.

llvm-svn: 160994

This function verifies the consistency of cached data in the
MachineTraceMetrics analysis.

llvm-svn: 160976

llvm-svn: 160905

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

It will surely be needed by heuristics.

llvm-svn: 160027

This ordering allows nested if-conversion without using a work list, and
it makes it possible to update the dominator tree on the fly as well.

Any erased basic blocks will always be dominated by the current
post-order position, so the domtree can be pruned without invalidating
the iterator.

llvm-svn: 160025

llvm-svn: 159800

from IfConversion.cc), and fix some spelling and grammar in the surrounding
prose.

llvm-svn: 159699

This pass performs if-conversion on SSA form machine code by
speculatively executing both sides of the branch and using a cmov
instruction to select the result. This can help lower the number of
branch mispredictions on architectures like x86 that don't have
predicable instructions.

The current implementation is very aggressive, and causes regressions on
mosts tests. It needs good heuristics that have yet to be implemented.

llvm-svn: 159694