forked from OSchip/llvm-project
fc02e3c363
Runtime unrolling will create a prologue to execute the extra iterations which is can't divided by the unroll factor. It generates an if-then-else sequence to jump into a factor -1 times unrolled loop body, like extraiters = tripcount % loopfactor if (extraiters == 0) jump Loop: if (extraiters == loopfactor) jump L1 if (extraiters == loopfactor-1) jump L2 ... L1: LoopBody; L2: LoopBody; ... if tripcount < loopfactor jump End Loop: ... End: It means if the unroll factor is 4, the loop body will be 7 times unrolled, 3 are in loop prologue, and 4 are in the loop. This commit is to use a loop to execute the extra iterations in prologue, like extraiters = tripcount % loopfactor if (extraiters == 0) jump Loop: else jump Prol Prol: LoopBody; extraiters -= 1 // Omitted if unroll factor is 2. if (extraiters != 0) jump Prol: // Omitted if unroll factor is 2. if (tripcount < loopfactor) jump End Loop: ... End: Then when unroll factor is 4, the loop body will be copied by only 5 times, 1 in the prologue loop, 4 in the original loop. And if the unroll factor is 2, new loop won't be created, just as the original solution. llvm-svn: 218604 |
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a2-unrolling.ll | ||
lit.local.cfg |