Use a loop to simplify the runtime unrolling prologue.
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
diff --git a/llvm/test/Transforms/LoopUnroll/runtime-loop2.ll b/llvm/test/Transforms/LoopUnroll/runtime-loop2.ll
index cbc7af5..7205c68 100644
--- a/llvm/test/Transforms/LoopUnroll/runtime-loop2.ll
+++ b/llvm/test/Transforms/LoopUnroll/runtime-loop2.ll
@@ -3,8 +3,7 @@
; Choose a smaller, power-of-two, unroll count if the loop is too large.
; This test makes sure we're not unrolling 'odd' counts
-; CHECK: unr.cmp:
-; CHECK: for.body.unr:
+; CHECK: for.body.prol:
; CHECK: for.body:
; CHECK: br i1 %exitcond.3, label %for.end.loopexit{{.*}}, label %for.body
; CHECK-NOT: br i1 %exitcond.4, label %for.end.loopexit{{.*}}, label %for.body