[llvm] [llvm-exegesis] Make duplicate snippet repetitor produce whole snippets (PR #77224)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 created https://github.com/llvm/llvm-project/pull/77224

Currently, the duplicate snippet repetitor will truncate snippets that do not exactly divide the minimum number of instructions. This patch corrects that behavior by making the duplicate snippet repetitor duplicate the snippet in its entirety until the minimum number of instructions has been reached.

>From de6ece982679c05c2e469f7f4bda37065d23d2f9 Mon Sep 17 00:00:00 2001
From: Aiden Grossman <agrossman154 at yahoo.com>
Date: Sat, 6 Jan 2024 22:30:25 -0800
Subject: [PATCH] [llvm-exegesis] Make duplicate snippet repetitor produce
 whole snippets

Currently, the duplicate snippet repetitor will truncate snippets that
do not exactly divide the minimum number of instructions. This patch
corrects that behavior by making the duplicate snippet repetitor
duplicate the snippet in its entirety until the minimum number of
instructions has been reached.
---
 .../llvm-exegesis/lib/SnippetRepetitor.cpp     |  6 +++++-
 .../llvm-exegesis/X86/SnippetRepetitorTest.cpp | 18 ++++++++++++++++--
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/llvm/tools/llvm-exegesis/lib/SnippetRepetitor.cpp b/llvm/tools/llvm-exegesis/lib/SnippetRepetitor.cpp
index cc5a045a8be5dd..5861d56c61cf6d 100644
--- a/llvm/tools/llvm-exegesis/lib/SnippetRepetitor.cpp
+++ b/llvm/tools/llvm-exegesis/lib/SnippetRepetitor.cpp
@@ -31,7 +31,11 @@ class DuplicateSnippetRepetitor : public SnippetRepetitor {
       if (!Instructions.empty()) {
         // Add the whole snippet at least once.
         Entry.addInstructions(Instructions);
-        for (unsigned I = Instructions.size(); I < MinInstructions; ++I) {
+        unsigned FullInstructionCount = MinInstructions;
+        if (FullInstructionCount % Instructions.size() != 0)
+          FullInstructionCount +=
+              Instructions.size() - (MinInstructions % Instructions.size());
+        for (unsigned I = Instructions.size(); I < FullInstructionCount; ++I) {
           Entry.addInstruction(Instructions[I % Instructions.size()]);
         }
       }
diff --git a/llvm/unittests/tools/llvm-exegesis/X86/SnippetRepetitorTest.cpp b/llvm/unittests/tools/llvm-exegesis/X86/SnippetRepetitorTest.cpp
index d2382ec0cddc49..25e8836087c15d 100644
--- a/llvm/unittests/tools/llvm-exegesis/X86/SnippetRepetitorTest.cpp
+++ b/llvm/unittests/tools/llvm-exegesis/X86/SnippetRepetitorTest.cpp
@@ -38,9 +38,11 @@ class X86SnippetRepetitorTest : public X86TestBase {
     MF = &createVoidVoidPtrMachineFunction("TestFn", Mod.get(), MMI.get());
   }
 
-  void TestCommon(Benchmark::RepetitionModeE RepetitionMode) {
+  void TestCommon(Benchmark::RepetitionModeE RepetitionMode,
+                  unsigned SnippetInstructions = 1) {
     const auto Repetitor = SnippetRepetitor::Create(RepetitionMode, State);
-    const std::vector<MCInst> Instructions = {MCInstBuilder(X86::NOOP)};
+    const std::vector<MCInst> Instructions(SnippetInstructions,
+                                           MCInstBuilder(X86::NOOP));
     FunctionFiller Sink(*MF, {X86::EAX});
     const auto Fill =
         Repetitor->Repeat(Instructions, kMinInstructions, kLoopBodySize, false);
@@ -74,6 +76,18 @@ TEST_F(X86SnippetRepetitorTest, Duplicate) {
                           HasOpcode(X86::NOOP), HasOpcode(X86::RET64)));
 }
 
+TEST_F(X86SnippetRepetitorTest, DuplicateSnippetInstructionCount) {
+  TestCommon(Benchmark::Duplicate, 2);
+  // Duplicating a snippet of two instructions with the minimum number of
+  // instructions set to three duplicates the snippet twice for a total of
+  // four instructions.
+  ASSERT_EQ(MF->getNumBlockIDs(), 1u);
+  EXPECT_THAT(MF->getBlockNumbered(0)->instrs(),
+              ElementsAre(HasOpcode(X86::NOOP), HasOpcode(X86::NOOP),
+                          HasOpcode(X86::NOOP), HasOpcode(X86::NOOP),
+                          HasOpcode(X86::RET64)));
+}
+
 TEST_F(X86SnippetRepetitorTest, Loop) {
   TestCommon(Benchmark::Loop);
   // Duplicating creates an entry block, a loop body and a ret block.