[MCA] Add flag -show-encoding to llvm-mca.

Flag -show-encoding enables the printing of instruction encodings as part of the
the instruction info view.

Example (with flags -mtriple=x86_64--  -mcpu=btver2):

Instruction Info:
[1]: #uOps
[2]: Latency
[3]: RThroughput
[4]: MayLoad
[5]: MayStore
[6]: HasSideEffects (U)
[7]: Encoding Size

[1]    [2]    [3]    [4]    [5]    [6]    [7]    Encodings:     Instructions:
 1      2     1.00                         4     c5 f0 59 d0    vmulps   %xmm0, %xmm1, %xmm2
 1      4     1.00                         4     c5 eb 7c da    vhaddps  %xmm2, %xmm2, %xmm3
 1      4     1.00                         4     c5 e3 7c e3    vhaddps  %xmm3, %xmm3, %xmm4

In this example, column Encoding Size is the size in bytes of the instruction
encoding. Column Encodings reports the actual instruction encodings as byte
sequences in hex (objdump style).

The computation of encodings is done by a utility class named mca::CodeEmitter.

In future, I plan to expose the CodeEmitter to the instruction builder, so that
information about instruction encoding sizes can be used by the simulator. That
would be a first step towards simulating the throughput from the decoders in the
hardware frontend.

Differential Revision: https://reviews.llvm.org/D65948

llvm-svn: 368432

2 files changed, 38 insertions, 0 deletions

diff --git a/llvm/lib/MCA/CMakeLists.txt b/llvm/lib/MCA/CMakeLists.txt
index 4965b6b31c1..e2eb06eb97c 100644
--- a/llvm/lib/MCA/CMakeLists.txt
+++ b/llvm/lib/MCA/CMakeLists.txt
@@ -1,4 +1,5 @@
 add_llvm_library(LLVMMCA
+  CodeEmitter.cpp
   Context.cpp
   HWEventListener.cpp
   HardwareUnits/HardwareUnit.cpp
diff --git a/llvm/lib/MCA/CodeEmitter.cpp b/llvm/lib/MCA/CodeEmitter.cpp
new file mode 100644
index 00000000000..294107219cb
--- /dev/null
+++ b/llvm/lib/MCA/CodeEmitter.cpp
@@ -0,0 +1,37 @@
+//===--------------------- CodeEmitter.cpp ----------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the CodeEmitter API.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/MCA/CodeEmitter.h"
+
+namespace llvm {
+namespace mca {
+
+CodeEmitter::EncodingInfo
+CodeEmitter::getOrCreateEncodingInfo(unsigned MCID) {
+  EncodingInfo &EI = Encodings[MCID];
+  if (EI.second)
+    return EI;
+
+  SmallVector<llvm::MCFixup, 2> Fixups;
+  const MCInst &Inst = Sequence[MCID];
+  MCInst Relaxed(Sequence[MCID]);
+  if (MAB.mayNeedRelaxation(Inst, STI))
+    MAB.relaxInstruction(Inst, STI, Relaxed);
+
+  EI.first = Code.size();
+  MCE.encodeInstruction(Relaxed, VecOS, Fixups, STI);
+  EI.second = Code.size() - EI.first;
+  return EI;
+}
+
+} // namespace mca
+} // namespace llvm