llvm-project/llvm/test/Transforms/LoopStrengthReduce
Wei Mi 90707394e3 [LSR] Narrow search space by filtering non-optimal formulae with the same ScaledReg and Scale.
When the formulae search space is huge, LSR uses a series of heuristic to keep
pruning the search space until the number of possible solutions are within
certain limit.

The big hammer of the series of heuristics is NarrowSearchSpaceByPickingWinnerRegs,
which picks the register which is used by the most LSRUses and deletes the other
formulae which don't use the register. This is a effective way to prune the search
space, but quite often not a good way to keep the best solution. We saw cases before
that the heuristic pruned the best formula candidate out of search space.

To relieve the problem, we introduce a new heuristic called
NarrowSearchSpaceByFilterFormulaWithSameScaledReg. The basic idea is in order to
reduce the search space while keeping the best formula, we want to keep as many
formulae with different Scale and ScaledReg as possible. That is because the central
idea of LSR is to choose a group of loop induction variables and use those induction
variables to represent LSRUses. An induction variable candidate is often represented
by the Scale and ScaledReg in a formula. If we have more formulae with different
ScaledReg and Scale to choose, we have better opportunity to find the best solution.
That is why we believe pruning search space by only keeping the best formula with the
same Scale and ScaledReg should be more effective than PickingWinnerReg. And we use
two criteria to choose the best formula with the same Scale and ScaledReg. The first
criteria is to select the formula using less non shared registers, and the second
criteria is to select the formula with less cost got from RateFormula. The patch
implements the heuristic before NarrowSearchSpaceByPickingWinnerRegs, which is the
last resort.

Testing shows we get 1.8% and 2% on two internal benchmarks on x86. llvm nightly
testsuite performance is neutral. We also tried lsr-exp-narrow and it didn't help
on the two improved internal cases we saw.

Differential Revision: https://reviews.llvm.org/D34583

llvm-svn: 307269
2017-07-06 15:52:14 +00:00
..
AArch64 Reapply [LSR] Create fewer redundant instructions. 2016-06-06 19:10:46 +00:00
AMDGPU AMDGPU: Mark all unspecified CC functions in tests as amdgpu_kernel 2017-03-21 21:39:51 +00:00
ARM ARM: handle post-indexed NEON ops where the offset isn't the access width. 2017-04-20 19:54:02 +00:00
NVPTX [NVPTX] truncating 64-bit to 32-bit is free 2015-08-20 20:59:02 +00:00
X86 [LSR] Narrow search space by filtering non-optimal formulae with the same ScaledReg and Scale. 2017-07-06 15:52:14 +00:00
2005-08-15-AddRecIV.ll
2005-08-17-OutOfLoopVariant.ll
2005-09-12-UsesOutOutsideOfLoop.ll
2007-04-23-UseIterator.ll
2008-08-13-CmpStride.ll
2008-09-09-Overflow.ll
2009-01-13-nonconstant-stride-outside-loop.ll
2009-04-28-no-reduce-mul.ll
2011-07-19-CritEdgeBreakCrash.ll
2011-10-03-CritEdgeMerge.ll
2011-10-06-ReusePhi.ll [LSR] canonicalize Prod*(1<<C) to Prod<<C 2015-06-24 19:28:40 +00:00
2011-10-13-SCEVChain.ll
2011-10-14-IntPtr.ll
2011-12-19-PostincQuadratic.ll
2012-01-02-nopreheader.ll
2012-01-16-nopreheader.ll
2012-03-15-nopreheader.ll
2012-03-26-constexpr.ll
2012-07-13-ExpandUDiv.ll
2012-07-18-LimitReassociate.ll
2013-01-05-IndBr.ll
2013-01-14-ReuseCast.ll [LSR] Narrow search space by filtering non-optimal formulae with the same ScaledReg and Scale. 2017-07-06 15:52:14 +00:00
addrec-gep-address-space.ll
addrec-gep.ll
address-space-loop.ll
count-to-zero.ll
dead-phi.ll
different-type-ivs.ll
dominate-assert.ll Move the personality function from LandingPadInst to Function 2015-06-17 20:52:32 +00:00
dont-hoist-simple-loop-constants.ll
dont_insert_redundant_ops.ll
dont_reduce_bytes.ll
dont_reverse.ll
ephemeral.ll [LSR] don't attempt to promote ephemeral values to indvars 2015-07-13 03:28:53 +00:00
exit_compare_live_range.ll
funclet.ll [LoopStrengthReduce] Don't rewrite PHIs with incoming values from CatchSwitches 2016-02-03 21:30:34 +00:00
hoist-parent-preheader.ll
invariant_value_first.ll
invariant_value_first_arg.ll
ivchain.ll [PM] Convert Loop Strength Reduce pass to new PM 2016-07-18 21:41:50 +00:00
negative-scale.ll
nested-reduce.ll
nonintegral.ll [SCEVExpander] Try harder to avoid introducing inttoptr 2017-05-27 03:22:55 +00:00
nonlinear-postinc.ll
ops_after_indvar.ll
phi_node_update_multiple_preds.ll
post-inc-icmpzero.ll Re-enable "[SCEV] Do not fold dominated SCEVUnknown into AddRecExpr start" 2017-05-26 06:47:04 +00:00
post-inc-optsize.ll [LSR] Don't try and create post-inc expressions on non-rotated loops 2016-08-15 07:53:03 +00:00
pr2537.ll
pr2570.ll
pr3086.ll
pr3399.ll
pr3571.ll
pr12018.ll DI: Require subprogram definitions to be distinct 2015-08-28 20:26:49 +00:00
pr12048.ll
pr12691.ll
pr18165.ll
pr25541.ll [IR] Reformulate LLVM's EH funclet IR 2015-12-12 05:38:55 +00:00
pr27056.ll [LoopStrengthReduce] Don't hoist into a catchswitch 2016-03-24 21:40:22 +00:00
pr31627.ll [LoopStrengthReduce] Don't bother rewriting PHIs in catchswitch blocks 2017-01-13 22:24:27 +00:00
preserve-gep-loop-variant.ll
related_indvars.ll
remove_indvar.ll
scaling_factor_cost_crash.ll
scev-insertpt-bug.ll Reapply [LSR] Create fewer redundant instructions. 2016-06-06 19:10:46 +00:00
sext-ind-var.ll [SCEV] Apply NSW and NUW flags via poison value analysis for sub, mul and shl 2015-08-14 22:45:26 +00:00
share_code_in_preheader.ll
share_ivs.ll
shl.ll [LSR] canonicalize Prod*(1<<C) to Prod<<C 2015-06-24 19:28:40 +00:00
uglygep-address-space.ll
uglygep.ll
use_postinc_value_outside_loop.ll
var_stride_used_by_compare.ll
variable_stride.ll