<div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Jun 3, 2015 at 9:13 AM, Johannes Doerfert <span dir="ltr"><<a href="mailto:doerfert@cs.uni-saarland.de" target="_blank">doerfert@cs.uni-saarland.de</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">Isnt't there a LLVM pass that will do this kind of optimization<br>
(Instcombine)?<br></blockquote><div><br></div><div>InstCombine optimizes signed divides to unsigned divides when doing so is obvious (both operands have a clear sign bit). Unsigned divides are then turned in shift right operations.</div><div><br></div><div>q = n / (2**k) is equivalent to (n >= 0 ? n : -n) >> k.<br></div><div><br></div><div>Modeling this in InstCombine would make it harder to analyze so we leave it to CodeGen to emit.</div><div><br></div><div><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
<div class=""><div class="h5"><br>
<br>
On 06/03, Tobias Grosser wrote:<br>
> Author: grosser<br>
> Date: Wed Jun 3 10:14:58 2015<br>
> New Revision: 238929<br>
><br>
> URL: <a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject-3Frev-3D238929-26view-3Drev&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=FBLHH8bJ-iDZ3gf9plCcxWjNABPLuAT6mA39ccnTpIs&s=hU4XCUVquLcFnNMfKx45_ifNUUZ2LwVSOD_HaHUyrYk&e=" target="_blank">http://llvm.org/viewvc/llvm-project?rev=238929&view=rev</a><br>
> Log:<br>
> Lower signed-divisions without rounding to ashr instructions<br>
><br>
> Modified:<br>
> polly/trunk/lib/CodeGen/IslExprBuilder.cpp<br>
> polly/trunk/test/Isl/CodeGen/exprModDiv.ll<br>
><br>
> Modified: polly/trunk/lib/CodeGen/IslExprBuilder.cpp<br>
> URL: <a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_polly_trunk_lib_CodeGen_IslExprBuilder.cpp-3Frev-3D238929-26r1-3D238928-26r2-3D238929-26view-3Ddiff&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=FBLHH8bJ-iDZ3gf9plCcxWjNABPLuAT6mA39ccnTpIs&s=E2nGeh_dQv83ki_knVf8YP7IJJY8n3aBYjgUB-1SGBU&e=" target="_blank">http://llvm.org/viewvc/llvm-project/polly/trunk/lib/CodeGen/IslExprBuilder.cpp?rev=238929&r1=238928&r2=238929&view=diff</a><br>
> ==============================================================================<br>
> --- polly/trunk/lib/CodeGen/IslExprBuilder.cpp (original)<br>
> +++ polly/trunk/lib/CodeGen/IslExprBuilder.cpp Wed Jun 3 10:14:58 2015<br>
> @@ -295,6 +295,13 @@ Value *IslExprBuilder::createOpBin(__isl<br>
> Res = Builder.CreateNSWMul(LHS, RHS);<br>
> break;<br>
> case isl_ast_op_div:<br>
> + if (auto *Const = dyn_cast<ConstantInt>(RHS)) {<br>
> + auto &Val = Const->getValue();<br>
> + if (Val.isPowerOf2() && Val.isNonNegative()) {<br>
> + Res = Builder.CreateAShr(LHS, Val.ceilLogBase2(), "pexp.div.shr");<br>
> + break;<br>
> + }<br>
> + }<br>
> Res = Builder.CreateSDiv(LHS, RHS, "pexp.div");<br>
> break;<br>
> case isl_ast_op_pdiv_q: // Dividend is non-negative<br>
><br>
> Modified: polly/trunk/test/Isl/CodeGen/exprModDiv.ll<br>
> URL: <a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_polly_trunk_test_Isl_CodeGen_exprModDiv.ll-3Frev-3D238929-26r1-3D238928-26r2-3D238929-26view-3Ddiff&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=FBLHH8bJ-iDZ3gf9plCcxWjNABPLuAT6mA39ccnTpIs&s=7s0plyAPweoz06g0qW6Xs7Fewc-cYEqyeSVcFgU7Q4w&e=" target="_blank">http://llvm.org/viewvc/llvm-project/polly/trunk/test/Isl/CodeGen/exprModDiv.ll?rev=238929&r1=238928&r2=238929&view=diff</a><br>
> ==============================================================================<br>
> --- polly/trunk/test/Isl/CodeGen/exprModDiv.ll (original)<br>
> +++ polly/trunk/test/Isl/CodeGen/exprModDiv.ll Wed Jun 3 10:14:58 2015<br>
> @@ -46,10 +46,8 @@<br>
> ; POW2: %polly.access.A6 = getelementptr float, float* %A, i64 %pexp.pdiv_r<br>
><br>
> ; A[i / 128]<br>
> -; POW2: %pexp.div = sdiv i64 %polly.indvar, 128<br>
> +; POW2: %pexp.div.shr = ashr i64 %polly.indvar, 7<br>
> ; POW2: %polly.access.B8 = getelementptr float, float* %B, i64 %pexp.div<br>
> -;<br>
> -; FIXME: Make isl mark this as an udiv expression.<br>
><br>
> ; #define floord(n,d) ((n < 0) ? (n - d + 1) : n) / d<br>
> ; A[p + 128 * floord(-p - 1, 128) + 128]<br>
> @@ -62,8 +60,8 @@<br>
> ; POW2: %polly.access.A10 = getelementptr float, float* %A, i64 %24<br>
><br>
> ; A[p / 128]<br>
> -; POW2: %pexp.div12 = sdiv i64 %p, 128<br>
> -; POW2: %polly.access.B13 = getelementptr float, float* %B, i64 %pexp.div12<br>
> +; POW2: %pexp.div.shr12 = ashr i64 %p, 7<br>
> +; POW2: %polly.access.B13 = getelementptr float, float* %B, i64 %pexp.div.shr12<br>
><br>
> target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"<br>
><br>
><br>
><br>
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<br>
</div></div><span class=""><font color="#888888">--<br>
<br>
Johannes Doerfert<br>
Researcher / PhD Student<br>
<br>
Compiler Design Lab (Prof. Hack)<br>
Saarland University, Computer Science<br>
Building E1.3, Room 4.31<br>
<br>
Tel. <a href="tel:%2B49%20%280%29681%20302-57521" value="+4968130257521">+49 (0)681 302-57521</a> : <a href="mailto:doerfert@cs.uni-saarland.de">doerfert@cs.uni-saarland.de</a><br>
Fax. <a href="tel:%2B49%20%280%29681%20302-3065" value="+496813023065">+49 (0)681 302-3065</a> : <a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__www.cdl.uni-2Dsaarland.de_people_doerfert&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=FBLHH8bJ-iDZ3gf9plCcxWjNABPLuAT6mA39ccnTpIs&s=ZNLkSig6JfcAUulThcZlt_JNsbhpYEnJmdotm8VS6gI&e=" target="_blank">http://www.cdl.uni-saarland.de/people/doerfert</a><br>
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<br></blockquote></div><br></div></div>