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another random note

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@47831 91177308-0d34-0410-b5e6-96231b3b80d8
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Chris Lattner 2008-03-02 19:29:42 +00:00
parent 150943c178
commit 53b7277917
1 changed files with 23 additions and 0 deletions
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23
lib/Target/README.txt
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@ -705,3 +705,26 @@ int f() {
}
//===---------------------------------------------------------------------===//
The loop unroller should partially unroll loops (instead of peeling them)
when code growth isn't too bad and when an unroll count allows simplification
of some code within the loop. One trivial example is:
#include <stdio.h>
int main() {
int nRet = 17;
int nLoop;
for ( nLoop = 0; nLoop < 1000; nLoop++ ) {
if ( nLoop & 1 )
nRet += 2;
else
nRet -= 1;
}
return nRet;
}
Unrolling by 2 would eliminate the '&1' in both copies, leading to a net
reduction in code size. The resultant code would then also be suitable for
exit value computation.
//===---------------------------------------------------------------------===//