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A short while ago I wrote about the strange loop unrolling behavior we encountered. The problem was that with -O3, the following loop does not get unrolled if the ifdef'ed dead code is not present. ------------------------------------ extern volatile int v1; int unroll() { int i; int v2 = 0; for(i = 0; i < 3; i++) { if (i == v2) { v1 = 1000; } else { v1 = 1001; }

I am having a strange problem with loop unrolling. Attached is a small example that demonstrates what happens. There is a for-loop with a known trip count, and some control flow inside the loop. If the condition of the control flow only depends on the loop index and loop invariant variables, the loop is not unrolled. However, if the condition involves potentially loop variant variables, the loop