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| -rw-r--r-- | lib/Target/README.txt | 23 |
1 files changed, 23 insertions, 0 deletions
diff --git a/lib/Target/README.txt b/lib/Target/README.txt index 80b00377ae..d477c82fbb 100644 --- a/lib/Target/README.txt +++ b/lib/Target/README.txt @@ -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. + +//===---------------------------------------------------------------------===// |