Krzysztof Parzyszek
2012-Dec-02 01:36 UTC
[LLVMdev] Predictive Commoning / Scalar Replacement
On 12/1/2012 7:10 PM, Nick Lewycky wrote:> > I don't know of any, but I was wondering if you could point me to the > paper that describes predictive commoning? I could only find the > second-order predictive commoning paper, which if I understand correctly > is a much newer and different algorithm.I think the original paper was some internal IBM publication. The idea is basically to reuse values loaded in previous loop iterations. For example for (i) { x += 2*t[i-1] - t[i+1]; } would become for (i) { tm1 = tz; // t-minus-1 = t-zero tz = tp1; // t-zero = t-plus-1 tp1 = t[i+1]; // t-plus-1 = load x += 2*tm1 - tp1; } -Krzysztof -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation
Krzysztof Parzyszek
2012-Dec-02 01:40 UTC
[LLVMdev] Predictive Commoning / Scalar Replacement
On 12/1/2012 7:36 PM, Krzysztof Parzyszek wrote:> > I think the original paper was some internal IBM publication.Here's what I believe to be the reference: K.O'Brien, B.Hay, J.Minish, H.Schaffer, B.Schloss, A.Shepherd, and M.Zaleski, "Advanced compiler technology for the RISC System/6000 Architecture," IBM RISC System/6000 Technology, SA23-2619, IBM Corp., 1990, pp. 154-161. -Krzysztof -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation
There is a non-internal techpub for this somewhere, though it escapes me. My recollection is that TPO (the middle end of XLC) had moved on to 2nd order predictive quite a while ago. At least, the implementation I saw 6+ years ago in TPO was much closer to what is described in the 2nd order paper. On Sat, Dec 1, 2012 at 8:36 PM, Krzysztof Parzyszek <kparzysz at codeaurora.org> wrote:> On 12/1/2012 7:10 PM, Nick Lewycky wrote: >> >> >> I don't know of any, but I was wondering if you could point me to the >> paper that describes predictive commoning? I could only find the >> second-order predictive commoning paper, which if I understand correctly >> is a much newer and different algorithm. > > > I think the original paper was some internal IBM publication. > > The idea is basically to reuse values loaded in previous loop iterations. > > For example > for (i) { > x += 2*t[i-1] - t[i+1]; > } > would become > for (i) { > tm1 = tz; // t-minus-1 = t-zero > tz = tp1; // t-zero = t-plus-1 > tp1 = t[i+1]; // t-plus-1 = load > x += 2*tm1 - tp1; > } > > -Krzysztof > > > -- > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by > The Linux Foundation > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
Krzysztof Parzyszek
2012-Dec-02 15:48 UTC
[LLVMdev] Predictive Commoning / Scalar Replacement
On 12/1/2012 10:38 PM, Daniel Berlin wrote:> There is a non-internal techpub for this somewhere, though it escapes me. > My recollection is that TPO (the middle end of XLC) had moved on to > 2nd order predictive quite a while ago. > > At least, the implementation I saw 6+ years ago in TPO was much closer > to what is described in the 2nd order paper.TPO never had any other predictive commoning. The TPO's implementation was written by the guy who wrote the paper (Arie). -Krzysztof -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation
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