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Hi Philip,</div>
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Many thanks for your suggestions! My next steps were implementing this function in the ARM backend, and then actually use it. But I will now look first what's in SelectionDAG and TLI, and see if I can use and generalise this (to provide a default here in TTI).</div>
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Thanks again,</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
Sjoerd.</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Philip Reames <listmail@philipreames.com><br>
<b>Sent:</b> 20 March 2019 17:55<br>
<b>To:</b> Sjoerd Meijer; llvm-commits@lists.llvm.org<br>
<b>Subject:</b> Re: [llvm] r356555 - [TTI] getMemcpyCost</font>
<div> </div>
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<div class="BodyFragment"><font size="2"><span style="font-size:11pt;">
<div class="PlainText">There's already a good amount of information about lowering cost<br>
scattered between SelectionDAG and TLI. It would be really nice if the<br>
default cost could be generalized to represent the default lowering<br>
while still allowing targets to override if needed.<br>
<br>
Philip<br>
<br>
On 3/20/19 7:15 AM, Sjoerd Meijer via llvm-commits wrote:<br>
> Author: sjoerdmeijer<br>
> Date: Wed Mar 20 07:15:46 2019<br>
> New Revision: 356555<br>
><br>
> URL: <a href="http://llvm.org/viewvc/llvm-project?rev=356555&view=rev">http://llvm.org/viewvc/llvm-project?rev=356555&view=rev</a><br>
> Log:<br>
> [TTI] getMemcpyCost<br>
><br>
> This adds new function getMemcpyCost to TTI so that the cost of a memcpy can be<br>
> modeled and queried. The default implementation returns Expensive, but targets<br>
> can override this function to model the cost more accurately.<br>
><br>
> Differential Revision: <a href="https://reviews.llvm.org/D59252">https://reviews.llvm.org/D59252</a><br>
><br>
> Added:<br>
> llvm/trunk/test/Analysis/CostModel/ARM/memcpy.ll<br>
> Modified:<br>
> llvm/trunk/include/llvm/Analysis/TargetTransformInfo.h<br>
> llvm/trunk/include/llvm/Analysis/TargetTransformInfoImpl.h<br>
><br>
> Modified: llvm/trunk/include/llvm/Analysis/TargetTransformInfo.h<br>
> URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/TargetTransformInfo.h?rev=356555&r1=356554&r2=356555&view=diff">
http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/TargetTransformInfo.h?rev=356555&r1=356554&r2=356555&view=diff</a><br>
> ==============================================================================<br>
> --- llvm/trunk/include/llvm/Analysis/TargetTransformInfo.h (original)<br>
> +++ llvm/trunk/include/llvm/Analysis/TargetTransformInfo.h Wed Mar 20 07:15:46 2019<br>
> @@ -246,6 +246,10 @@ public:<br>
> ArrayRef<const Value *> Arguments,<br>
> const User *U = nullptr) const;<br>
> <br>
> + /// \Return the expected cost of a memcpy, which could e.g. depend on the<br>
> + /// source/destination type and alignment and the number of bytes copied.<br>
> + int getMemcpyCost(const Instruction *I) const;<br>
> +<br>
> /// \return The estimated number of case clusters when lowering \p 'SI'.<br>
> /// \p JTSize Set a jump table size only when \p SI is suitable for a jump<br>
> /// table.<br>
> @@ -1053,6 +1057,7 @@ public:<br>
> virtual int getIntrinsicCost(Intrinsic::ID IID, Type *RetTy,<br>
> ArrayRef<const Value *> Arguments,<br>
> const User *U) = 0;<br>
> + virtual int getMemcpyCost(const Instruction *I) = 0;<br>
> virtual unsigned getEstimatedNumberOfCaseClusters(const SwitchInst &SI,<br>
> unsigned &JTSize) = 0;<br>
> virtual int<br>
> @@ -1267,6 +1272,9 @@ public:<br>
> const User *U = nullptr) override {<br>
> return Impl.getIntrinsicCost(IID, RetTy, Arguments, U);<br>
> }<br>
> + int getMemcpyCost(const Instruction *I) {<br>
> + return Impl.getMemcpyCost(I);<br>
> + }<br>
> int getUserCost(const User *U, ArrayRef<const Value *> Operands) override {<br>
> return Impl.getUserCost(U, Operands);<br>
> }<br>
><br>
> Modified: llvm/trunk/include/llvm/Analysis/TargetTransformInfoImpl.h<br>
> URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/TargetTransformInfoImpl.h?rev=356555&r1=356554&r2=356555&view=diff">
http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/TargetTransformInfoImpl.h?rev=356555&r1=356554&r2=356555&view=diff</a><br>
> ==============================================================================<br>
> --- llvm/trunk/include/llvm/Analysis/TargetTransformInfoImpl.h (original)<br>
> +++ llvm/trunk/include/llvm/Analysis/TargetTransformInfoImpl.h Wed Mar 20 07:15:46 2019<br>
> @@ -140,15 +140,22 @@ public:<br>
> <br>
> unsigned getInliningThresholdMultiplier() { return 1; }<br>
> <br>
> + unsigned getMemcpyCost(const Instruction *I) {<br>
> + return TTI::TCC_Expensive;<br>
> + }<br>
> +<br>
> unsigned getIntrinsicCost(Intrinsic::ID IID, Type *RetTy,<br>
> ArrayRef<Type *> ParamTys, const User *U) {<br>
> switch (IID) {<br>
> default:<br>
> // Intrinsics rarely (if ever) have normal argument setup constraints.<br>
> // Model them as having a basic instruction cost.<br>
> - // FIXME: This is wrong for libc intrinsics.<br>
> return TTI::TCC_Basic;<br>
> <br>
> + // TODO: other libc intrinsics.<br>
> + case Intrinsic::memcpy:<br>
> + return getMemcpyCost(dyn_cast<Instruction>(U));<br>
> +<br>
> case Intrinsic::annotation:<br>
> case Intrinsic::assume:<br>
> case Intrinsic::sideeffect:<br>
><br>
> Added: llvm/trunk/test/Analysis/CostModel/ARM/memcpy.ll<br>
> URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/CostModel/ARM/memcpy.ll?rev=356555&view=auto">
http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/CostModel/ARM/memcpy.ll?rev=356555&view=auto</a><br>
> ==============================================================================<br>
> --- llvm/trunk/test/Analysis/CostModel/ARM/memcpy.ll (added)<br>
> +++ llvm/trunk/test/Analysis/CostModel/ARM/memcpy.ll Wed Mar 20 07:15:46 2019<br>
> @@ -0,0 +1,13 @@<br>
> +; RUN: opt < %s -cost-model -analyze -cost-kind=code-size | FileCheck %s<br>
> +<br>
> +target datalayout = "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64"<br>
> +target triple = "thumbv7m-arm-unknown-eabi"<br>
> +<br>
> +define void @memcpy(i8* %d, i8* %s, i32 %N) {<br>
> +entry:<br>
> +; CHECK: cost of 4 for instruction: call void @llvm.memcpy.p0i8.p0i8.i32<br>
> + call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 1 %d, i8* align 1 %s, i32 36, i1 false)<br>
> + ret void<br>
> +}<br>
> +<br>
> +declare void @llvm.memcpy.p0i8.p0i8.i32(i8* nocapture writeonly, i8* nocapture readonly, i32, i1) #1<br>
><br>
><br>
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