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add a note about a SPEC hack that gcc mainline does.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121849 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2010-12-15 06:38:24 +00:00
parent 33e77d3cb9
commit 2fc36e19b1
1 changed files with 23 additions and 0 deletions
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lib/Target/README.txt
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@ -1226,6 +1226,29 @@ loadpre14.c loadpre15.c
actually a conditional increment: loadpre18.c loadpre19.c
//===---------------------------------------------------------------------===//
[LOAD PRE / STORE SINKING / SPEC HACK]
This is a chunk of code from 456.hmmer:
int f(int M, int *mc, int *mpp, int *tpmm, int *ip, int *tpim, int *dpp,
int *tpdm, int xmb, int *bp, int *ms) {
int k, sc;
for (k = 1; k <= M; k++) {
mc[k] = mpp[k-1] + tpmm[k-1];
if ((sc = ip[k-1] + tpim[k-1]) > mc[k]) mc[k] = sc;
if ((sc = dpp[k-1] + tpdm[k-1]) > mc[k]) mc[k] = sc;
if ((sc = xmb + bp[k]) > mc[k]) mc[k] = sc;
mc[k] += ms[k];
}
}
It is very profitable for this benchmark to turn the conditional stores to mc[k]
into a conditional move (select instr in IR) and allow the final store to do the
store. See GCC PR27313 for more details. Note that this is valid to xform even
with the new C++ memory model, since mc[k] is previously loaded and later
stored.
//===---------------------------------------------------------------------===//