[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

1 files changed, 33 insertions, 4 deletions

diff --git a/llvm/docs/CommandGuide/llvm-mca.rst b/llvm/docs/CommandGuide/llvm-mca.rst
index f2ebbec43c0..4f8704ad9a9 100644
--- a/llvm/docs/CommandGuide/llvm-mca.rst
+++ b/llvm/docs/CommandGuide/llvm-mca.rst
@@ -174,6 +174,10 @@ option specifies "``-``", then the output will also be sent to standard output.
 
   Enable the instruction info view. This is enabled by default.
 
+.. option:: -show-encoding
+
+  Enable the printing of instruction encodings within the instruction info view.
+
 .. option:: -all-stats
 
   Print all hardware statistics. This enables extra statistics related to the
@@ -415,10 +419,10 @@ an indicator of a performance bottleneck caused by the lack of hardware
 resources, and the *Resource pressure view* can help to identify the problematic
 resource usage.
 
-The second section of the report shows the latency and reciprocal
-throughput of every instruction in the sequence. That section also reports
-extra information related to the number of micro opcodes, and opcode properties
-(i.e., 'MayLoad', 'MayStore', and 'HasSideEffects').
+The second section of the report is the `instruction info view`. It shows the
+latency and reciprocal throughput of every instruction in the sequence. It also
+reports extra information related to the number of micro opcodes, and opcode
+properties (i.e., 'MayLoad', 'MayStore', and 'HasSideEffects').
 
 Field *RThroughput* is the reciprocal of the instruction throughput. Throughput
 is computed as the maximum number of instructions of a same type that can be
@@ -427,6 +431,31 @@ example, the reciprocal throughput of a vector float multiply is 1
 cycles/instruction.  That is because the FP multiplier JFPM is only available
 from pipeline JFPU1.
 
+Instruction encodings are displayed within the instruction info view when flag
+`-show-encoding` is specified.
+
+Below is an example of `-show-encoding` output for the dot-product kernel:
+
+.. code-block:: none
+
+  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
+
+The `Encoding Size` column shows the size in bytes of instructions.  The
+`Encodings` column shows the actual instruction encodings (byte sequences in
+hex).
+
 The third section is the *Resource pressure view*.  This view reports
 the average number of resource cycles consumed every iteration by instructions
 for every processor resource unit available on the target.  Information is