http://llvm.org/bugs/show_bug.cgi?id=14076
Bug #: 14076
Summary: Problems highlighted by the TSVC loop benchmarks
Product: libraries
Version: trunk
Platform: PC
OS/Version: All
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: X86
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
Classification: Unclassified
On the general assumption that running the TSVC loops with floats should be
faster than running them with doubles, I suspect we have suboptimal code
generation for the following tests:
[from: http://llvm.org/perf/db_default/v4/nts/4826]
MultiSource/Benchmarks/TSVC/ControlLoops-dbl/ControlLoops-dbl 5.3408
MultiSource/Benchmarks/TSVC/ControlLoops-flt/ControlLoops-flt 6.6713
MultiSource/Benchmarks/TSVC/Reductions-dbl/Reductions-dbl 5.4195
MultiSource/Benchmarks/TSVC/Reductions-flt/Reductions-flt 8.6970
Also, while the double-precision code should be slower, as we're not
vectorizing, can it legitimately be 2x slower? If not, these also indicate a
problem:
MultiSource/Benchmarks/TSVC/Expansion-dbl/Expansion-dbl 7.1848
MultiSource/Benchmarks/TSVC/Expansion-flt/Expansion-flt 4.3780
MultiSource/Benchmarks/TSVC/LoopRestructuring-dbl/LoopRestructuring-dbl
8.3210
MultiSource/Benchmarks/TSVC/LoopRestructuring-flt/LoopRestructuring-flt
4.2134
These also seems questionable:
MultiSource/Benchmarks/TSVC/NodeSplitting-dbl/NodeSplitting-dbl 8.5494
MultiSource/Benchmarks/TSVC/NodeSplitting-flt/NodeSplitting-flt 5.5331
MultiSource/Benchmarks/TSVC/Symbolics-dbl/Symbolics-dbl 4.9180
MultiSource/Benchmarks/TSVC/Symbolics-flt/Symbolics-flt 3.5667
When these tests are run on my POWER7 (powerpc64) machine, the timing on the
tests is as I would expect: the float and double versions take approximately
the same amount of time to execute, with the double-precision version generally
taking slightly more time. As a result, I suspect that these problems are
specific to x86 codegen.
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