Summary:
This patch adds MachineCombiner patterns for transforming
(fsub (fmul x y) z) into (fma x y (fneg z)). This has a lower
latency on micro architectures where fneg is cheap.
Patch based on work by George Steed.
Reviewers: rengolin, joelkevinjones, joel_k_jones, evandro, efriedma
Reviewed By: evandro
Subscribers: aemerson, javed.absar, llvm-commits, kristof.beyls
Differential Revision: https://reviews.llvm.org/D40306
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@319980 91177308-0d34-0410-b5e6-96231b3b80d8
The original patch caused crashes because it could derefence a null pointer
for SelectionDAGTargetInfo for targets that do not define it.
Evaluates fmul+fadd -> fmadd combines and similar code sequences in the
machine combiner. It adds support for float and double similar to the existing
integer implementation. The key features are:
- DAGCombiner checks whether it should combine greedily or let the machine
combiner do the evaluation. This is only supported on ARM64.
- It gives preference to throughput over latency: the heuristic used is
to combine always in loops. The targets decides whether the machine
combiner should optimize for throughput or latency.
- Supports for fmadd, f(n)msub, fmla, fmls patterns
- On by default at O3 ffast-math
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@267328 91177308-0d34-0410-b5e6-96231b3b80d8
Evaluates fmul+fadd -> fmadd combines and similar code sequences in the
machine combiner. It adds support for float and double similar to the existing
integer implementation. The key features are:
- DAGCombiner checks whether it should combine greedily or let the machine
combiner do the evaluation. This is only supported on ARM64.
- It gives preference to throughput over latency: the heuristic used is
to combine always in loops. The targets decides whether the machine
combiner should optimize for throughput or latency.
- Supports for fmadd, f(n)msub, fmla, fmls patterns
- On by default at O3 ffast-math
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@267098 91177308-0d34-0410-b5e6-96231b3b80d8
Also, remove an enum hack where enum values were used as indexes into an array.
We may want to make this a real class to allow pattern-based queries/customization (D13417).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@252196 91177308-0d34-0410-b5e6-96231b3b80d8
sequence - target independent framework
When the DAGcombiner selects instruction sequences
it could increase the critical path or resource len.
For example, on arm64 there are multiply-accumulate instructions (madd,
msub). If e.g. the equivalent multiply-add sequence is not on the
crictial path it makes sense to select it instead of the combined,
single accumulate instruction (madd/msub). The reason is that the
conversion from add+mul to the madd could lengthen the critical path
by the latency of the multiply.
But the DAGCombiner would always combine and select the madd/msub
instruction.
This patch uses machine trace metrics to estimate critical path length
and resource length of an original instruction sequence vs a combined
instruction sequence and picks the faster code based on its estimates.
This patch only commits the target independent framework that evaluates
and selects code sequences. The machine instruction combiner is turned
off for all targets and expected to evolve over time by gradually
handling DAGCombiner pattern in the target specific code.
This framework lays the groundwork for fixing
rdar://16319955
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214666 91177308-0d34-0410-b5e6-96231b3b80d8
