[llvm-exegesis] Make duplicate snippet repetitor produce whole snippets

[boomanaiden154]

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.

This makes the behavior consistent with the loop snippet repetitor, which will execute at least --num-repetitions (soon to be renamed --min-instructions) instructions.

[llvmbot]

@llvm/pr-subscribers-tools-llvm-exegesis

Author: Aiden Grossman (boomanaiden154)

Changes

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.

---

Full diff: https://github.com/llvm/llvm-project/pull/77224.diff

2 Files Affected:

• (modified) llvm/tools/llvm-exegesis/lib/SnippetRepetitor.cpp (+5-1)
• (modified) llvm/unittests/tools/llvm-exegesis/X86/SnippetRepetitorTest.cpp (+16-2)

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.

[legrosbuffle]

Thanks