[llvm] r284012 - NFC: The Cost Model specialization, by Andrey Tischenko
Alexey Bataev via llvm-commits
llvm-commits at lists.llvm.org
Wed Oct 12 06:24:13 PDT 2016
Author: abataev
Date: Wed Oct 12 08:24:13 2016
New Revision: 284012
URL: http://llvm.org/viewvc/llvm-project?rev=284012&view=rev
Log:
NFC: The Cost Model specialization, by Andrey Tischenko
The current Cost Model implementation is very inaccurate and has to be
updated, improved, re-implemented to be able to take into account the
concrete CPU models and the concrete targets where this Cost Model is
being used. For example, the Latency Cost Model should be differ from
Code Size Cost Model, etc.
This patch is the first step to launch the developing and implementation
of a new Cost Model generation.
Differential Revision: https://reviews.llvm.org/D25186
Modified:
llvm/trunk/lib/Target/X86/X86TargetTransformInfo.cpp
Modified: llvm/trunk/lib/Target/X86/X86TargetTransformInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86TargetTransformInfo.cpp?rev=284012&r1=284011&r2=284012&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86TargetTransformInfo.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86TargetTransformInfo.cpp Wed Oct 12 08:24:13 2016
@@ -13,6 +13,31 @@
/// independent and default TTI implementations handle the rest.
///
//===----------------------------------------------------------------------===//
+/// About Cost Model numbers used below it's necessary to say the following:
+/// the numbers correspond to some "generic" X86 CPU instead of usage of
+/// concrete CPU model. Usually the numbers correspond to CPU where the feature
+/// apeared at the first time. For example, if we do Subtarget.hasSSE42() in
+/// the lookups below the cost is based on Nehalem as that was the first CPU
+/// to support that feature level and thus has most likely the worst case cost.
+/// Some examples of other technologies/CPUs:
+/// SSE 3 - Pentium4 / Athlon64
+/// SSE 4.1 - Penryn
+/// SSE 4.2 - Nehalem
+/// AVX - Sandy Bridge
+/// AVX2 - Haswell
+/// AVX-512 - Xeon Phi / Skylake
+/// And some examples of instruction target dependent costs (latency)
+/// divss sqrtss rsqrtss
+/// AMD K7 11-16 19 3
+/// Piledriver 9-24 13-15 5
+/// Jaguar 14 16 2
+/// Pentium II,III 18 30 2
+/// Nehalem 7-14 7-18 3
+/// Haswell 10-13 11 5
+/// TODO: Develop and implement the target dependent cost model and
+/// specialize cost numbers for different Cost Model Targets such as throughput,
+/// code size, latency and uop count.
+//===----------------------------------------------------------------------===//
#include "X86TargetTransformInfo.h"
#include "llvm/Analysis/TargetTransformInfo.h"
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