Instead of stacking copies for both parent on the head, we move copies outside

of the heap into a dedicated dictionary. The two side of merge can we merged

sooner, making the algorithm simpler.

This simplicity reflect in the heap structure and speed up the execution for

copies involving a large amount of merges.

Here are timing for perfpathcopies of multiple revision pairs.

- filelog: timing using filelog (with the introrev condition dropped)
- base: this series base
- before: the parent of this changeset
- after: this changeset

revision: large amount; added files: large amount; rename small amount; c3b14617fbd7 9ba6ab77fd29

filelog: ! wall 3.679613 comb 3.680000 user 3.580000 sys 0.100000 (median of 3)

base: ! wall 8.884369 comb 8.880000 user 8.850000 sys 0.030000 (median of 3)

before: ! wall 8.443747 comb 8.420000 user 8.410000 sys 0.010000 (median of 3)

after: ! wall 4.697917 comb 4.690000 user 4.660000 sys 0.030000 (median of 3)

revision: large amount; added files: small amount; rename small amount; c3b14617fbd7 f650a9b140d2

filelog: ! wall 0.003357 comb 0.010000 user 0.010000 sys 0.000000 (median of 781)

base: ! wall 12.398524 comb 12.400000 user 12.330000 sys 0.070000 (median of 3)

before: ! wall 10.852593 comb 10.850000 user 10.800000 sys 0.050000 (median of 3)

after: ! wall 6.750832 comb 6.750000 user 6.640000 sys 0.110000 (median of 3)

revision: large amount; added files: large amount; rename large amount; 08ea3258278e d9fa043f30c0

filelog: ! wall 2.754687 comb 2.760000 user 2.650000 sys 0.110000 (median of 4)

base: ! wall 1.423166 comb 1.420000 user 1.400000 sys 0.020000 (median of 8)

before: ! wall 1.068041 comb 1.060000 user 1.050000 sys 0.010000 (median of 10)

after: ! wall 1.045916 comb 1.050000 user 1.040000 sys 0.010000 (median of 10)

revision: small amount; added files: large amount; rename large amount; df6f7a526b60 a83dc6a2d56f

filelog: ! wall 1.552293 comb 1.550000 user 1.510000 sys 0.040000 (median of 6

base: ! wall 0.022662 comb 0.020000 user 0.020000 sys 0.000000 (median of 128)

before: ! wall 0.021111 comb 0.020000 user 0.020000 sys 0.000000 (median of 139)

after: ! wall 0.021577 comb 0.020000 user 0.020000 sys 0.000000 (median of 138)

revision: small amount; added files: large amount; rename small amount; 4aa4e1f8e19a 169138063d63

filelog: ! wall 1.500983 comb 1.500000 user 1.420000 sys 0.080000 (median of 7)

base: ! wall 0.006956 comb 0.010000 user 0.010000 sys 0.000000 (median of 392)

before: ! wall 0.004356 comb 0.010000 user 0.010000 sys 0.000000 (median of 675)

after: ! wall 0.004329 comb 0.000000 user 0.000000 sys 0.000000 (median of 682)

revision: small amount; added files: small amount; rename small amount; 4bc173b045a6 964879152e2e

filelog: ! wall 0.011745 comb 0.020000 user 0.020000 sys 0.000000 (median of 250)

base: ! wall 0.000156 comb 0.000000 user 0.000000 sys 0.000000 (median of 17180)

before: ! wall 0.000100 comb 0.000000 user 0.000000 sys 0.000000 (median of 26912)

after: ! wall 0.000105 comb 0.000000 user 0.000000 sys 0.000000 (median of 25689)

revision: medium amount; added files: large amount; rename medium amount; c95f1ced15f2 2c68e87c3efe

filelog: ! wall 3.228230 comb 3.230000 user 3.110000 sys 0.120000 (median of 4)

base: ! wall 0.997640 comb 1.000000 user 0.980000 sys 0.020000 (median of 10)

before: ! wall 0.778291 comb 0.780000 user 0.780000 sys 0.000000 (median of 13)

after: ! wall 0.706594 comb 0.710000 user 0.710000 sys 0.000000 (median of 15)

revision: medium amount; added files: medium amount; rename small amount; d343da0c55a8 d7746d32bf9d

filelog: ! wall 1.052501 comb 1.060000 user 1.040000 sys 0.020000 (median of 10

base: ! wall 0.214519 comb 0.220000 user 0.220000 sys 0.000000 (median of 45)

before: ! wall 0.160804 comb 0.160000 user 0.160000 sys 0.000000 (median of 62)

after: ! wall 0.163736 comb 0.160000 user 0.160000 sys 0.000000 (median of 60)

list(roots)is simpler and clearer to me