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Actually adding the test file
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@ABenC377
ABenC377 committed Dec 9, 2024
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297 changes: 297 additions & 0 deletions test/unit/TagePredictorTest.cc
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#include "MockInstruction.hh"
#include "gtest/gtest.h"
#include "simeng/branchpredictors/TagePredictor.hh"

namespace simeng {

class TagePredictorTest : public testing::Test {
public:
TagePredictorTest() : uop(new MockInstruction), uopPtr(uop) {
uop->setInstructionAddress(0);
}

protected:
MockInstruction* uop;
std::shared_ptr<Instruction> uopPtr;
};

// Tests that TagePredictor will predict the correct direction on a miss
TEST_F(TagePredictorTest, Miss) {
simeng::config::SimInfo::addToConfig(
"{Branch-Predictor: "
" {Type: Tage, "
" BTB-Tag-Bits: 11, "
" Saturating-Count-Bits: 2, "
" Global-History-Length: 10, "
" RAS-entries: 5,"
" Fallback-Static-Predictor: Always-Taken,"
" Tage-Table-Bits: 12,"
" Num-Tage-Tables: 6,"
" Tag-Length: 8"
" }"
"}");
auto predictor = simeng::TagePredictor();
auto prediction = predictor.predict(0, BranchType::Conditional, 0);
EXPECT_TRUE(prediction.isTaken);
prediction = predictor.predict(8, BranchType::Unconditional, 0);
EXPECT_TRUE(prediction.isTaken);
}

// Tests that TagePredictor will predict branch-and-link return pairs correctly
TEST_F(TagePredictorTest, RAS) {
simeng::config::SimInfo::addToConfig(
"{Branch-Predictor: "
" {Type: Tage, "
" BTB-Tag-Bits: 11, "
" Saturating-Count-Bits: 2, "
" Global-History-Length: 10, "
" RAS-entries: 5,"
" Fallback-Static-Predictor: Always-Taken,"
" Tage-Table-Bits: 12,"
" Num-Tage-Tables: 6,"
" Tag-Length: 8"
" }"
"}");
auto predictor = simeng::TagePredictor();
auto prediction = predictor.predict(8, BranchType::SubroutineCall, 8);
EXPECT_TRUE(prediction.isTaken);
EXPECT_EQ(prediction.target, 16);
prediction = predictor.predict(24, BranchType::SubroutineCall, 8);
EXPECT_TRUE(prediction.isTaken);
EXPECT_EQ(prediction.target, 32);
prediction = predictor.predict(40, BranchType::SubroutineCall, 8);
EXPECT_TRUE(prediction.isTaken);
EXPECT_EQ(prediction.target, 48);
prediction = predictor.predict(56, BranchType::SubroutineCall, 8);
EXPECT_TRUE(prediction.isTaken);
EXPECT_EQ(prediction.target, 64);
prediction = predictor.predict(72, BranchType::SubroutineCall, 8);
EXPECT_TRUE(prediction.isTaken);
EXPECT_EQ(prediction.target, 80);

prediction = predictor.predict(84, BranchType::Return, 0);
EXPECT_TRUE(prediction.isTaken);
EXPECT_EQ(prediction.target, 76);
prediction = predictor.predict(68, BranchType::Return, 0);
EXPECT_TRUE(prediction.isTaken);
EXPECT_EQ(prediction.target, 60);
prediction = predictor.predict(52, BranchType::Return, 0);
EXPECT_TRUE(prediction.isTaken);
EXPECT_EQ(prediction.target, 44);
prediction = predictor.predict(36, BranchType::Return, 0);
EXPECT_TRUE(prediction.isTaken);
EXPECT_EQ(prediction.target, 28);
prediction = predictor.predict(20, BranchType::Return, 0);
EXPECT_TRUE(prediction.isTaken);
EXPECT_EQ(prediction.target, 12);
}

// Tests that TagePredictor will predict a previously encountered
// branch correctly, when no address aliasing has occurred
TEST_F(TagePredictorTest, Hit) {
simeng::config::SimInfo::addToConfig(
"{Branch-Predictor: "
" {Type: Tage, "
" BTB-Tag-Bits: 11, "
" Saturating-Count-Bits: 2, "
" Global-History-Length: 10, "
" RAS-entries: 5,"
" Fallback-Static-Predictor: Always-Taken,"
" Tage-Table-Bits: 12,"
" Num-Tage-Tables: 6,"
" Tag-Length: 8"
" }"
"}");
auto predictor = simeng::TagePredictor();
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, true, 16, BranchType::Conditional, 0);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, true, 16, BranchType::Conditional, 1);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, true, 16, BranchType::Conditional, 2);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, true, 16, BranchType::Conditional, 3);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, true, 16, BranchType::Conditional, 4);

auto prediction = predictor.predict(0, BranchType::Conditional, 0);
EXPECT_TRUE(prediction.isTaken);
EXPECT_EQ(prediction.target, 16);
}

// Tests that TagePredictor will predict correctly for two different
// behaviours of the same branch but in different states of the program
TEST_F(TagePredictorTest, GlobalIndexing) {
simeng::config::SimInfo::addToConfig(
"{Branch-Predictor: "
" {Type: Tage, "
" BTB-Tag-Bits: 11, "
" Saturating-Count-Bits: 2, "
" Global-History-Length: 10, "
" RAS-entries: 5,"
" Fallback-Static-Predictor: Always-Taken,"
" Tage-Table-Bits: 5,"
" Num-Tage-Tables: 1,"
" Tag-Length: 8"
" }"
"}");
auto predictor = simeng::TagePredictor();
// Spool up first global history pattern
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, true, 4, BranchType::Conditional, 0);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, false, 4, BranchType::Conditional, 1);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, false, 4, BranchType::Conditional, 2);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, false, 4, BranchType::Conditional, 3);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, true, 4, BranchType::Conditional, 4);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, true, 4, BranchType::Conditional, 5);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, false, 4, BranchType::Conditional, 6);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, false, 4, BranchType::Conditional, 7);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, false, 4, BranchType::Conditional, 8);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, true, 4, BranchType::Conditional, 9);
// Ensure default behaviour for first encounter
auto prediction = predictor.predict(0x7C, BranchType::Conditional, 0);
EXPECT_TRUE(prediction.isTaken);
EXPECT_EQ(prediction.target, 0);
// Set entry in BTB
predictor.update(0x7C, false, 0x80, BranchType::Conditional, 10);

// Spool up second global history pattern
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, false, 4, BranchType::Conditional, 11);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, true, 4, BranchType::Conditional, 12);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, true, 4, BranchType::Conditional, 13);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, true, 4, BranchType::Conditional, 14);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, false, 4, BranchType::Conditional, 15);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, false, 4, BranchType::Conditional, 16);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, true, 4, BranchType::Conditional, 17);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, true, 4, BranchType::Conditional, 18);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, true, 4, BranchType::Conditional, 19);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, false, 4, BranchType::Conditional, 20);
// Ee-encounter but with different global history
prediction = predictor.predict(0x7C, BranchType::Conditional, 0);
EXPECT_FALSE(prediction.isTaken);
EXPECT_EQ(prediction.target, 0x80);
// Set entry in BTB
predictor.update(0x7C, true, 0xBA, BranchType::Conditional, 21);

// Recreate first global history pattern
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, true, 4, BranchType::Conditional, 22);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, false, 4, BranchType::Conditional, 23);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, false, 4, BranchType::Conditional, 24);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, false, 4, BranchType::Conditional, 25);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, true, 4, BranchType::Conditional, 26);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, true, 4, BranchType::Conditional, 27);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, false, 4, BranchType::Conditional, 28);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, false, 4, BranchType::Conditional, 29);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, false, 4, BranchType::Conditional, 30);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, true, 4, BranchType::Conditional, 31);
// Get prediction
prediction = predictor.predict(0x7C, BranchType::Conditional, 0);
EXPECT_TRUE(prediction.isTaken);
EXPECT_EQ(prediction.target, 0xBA);
// Set entry in BTB
predictor.update(0x7C, true, 0x80, BranchType::Conditional, 32);

// Recreate second global history pattern
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, false, 4, BranchType::Conditional, 33);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, true, 4, BranchType::Conditional, 34);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, true, 4, BranchType::Conditional, 35);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, true, 4, BranchType::Conditional, 36);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, false, 4, BranchType::Conditional, 37);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, false, 4, BranchType::Conditional, 38);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, true, 4, BranchType::Conditional, 39);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, true, 4, BranchType::Conditional, 40);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, true, 4, BranchType::Conditional, 41);
predictor.predict(0, BranchType::Conditional, 0);
predictor.update(0, false, 4, BranchType::Conditional, 42);
// Get prediction
prediction = predictor.predict(0x7C, BranchType::Conditional, 0);
EXPECT_TRUE(prediction.isTaken);
EXPECT_EQ(prediction.target, 0x80);
predictor.update(0x7C, true, 0xBA, BranchType::Conditional, 43);
}

// Test Flush of RAS functionality
TEST_F(TagePredictorTest, flush) {
simeng::config::SimInfo::addToConfig(
"{Branch-Predictor: "
" {Type: Tage, "
" BTB-Tag-Bits: 11, "
" Saturating-Count-Bits: 2, "
" Global-History-Length: 10, "
" RAS-entries: 5,"
" Fallback-Static-Predictor: Always-Taken,"
" Tage-Table-Bits: 12,"
" Num-Tage-Tables: 1,"
" Tag-Length: 8"
" }"
"}");
auto predictor = simeng::TagePredictor();
// Add some entries to the RAS
auto prediction = predictor.predict(8, BranchType::SubroutineCall, 8);
EXPECT_TRUE(prediction.isTaken);
EXPECT_EQ(prediction.target, 16);
prediction = predictor.predict(24, BranchType::SubroutineCall, 8);
EXPECT_TRUE(prediction.isTaken);
EXPECT_EQ(prediction.target, 32);
prediction = predictor.predict(40, BranchType::SubroutineCall, 8);
EXPECT_TRUE(prediction.isTaken);
EXPECT_EQ(prediction.target, 48);

// Start getting entries from RAS
prediction = predictor.predict(52, BranchType::Return, 0);
EXPECT_TRUE(prediction.isTaken);
EXPECT_EQ(prediction.target, 44);
prediction = predictor.predict(36, BranchType::Return, 0);
EXPECT_TRUE(prediction.isTaken);
EXPECT_EQ(prediction.target, 28);

// Flush address
predictor.flush(36);

// Continue getting entries from RAS
prediction = predictor.predict(20, BranchType::Return, 0);
EXPECT_TRUE(prediction.isTaken);
EXPECT_EQ(prediction.target, 28);
prediction = predictor.predict(16, BranchType::Return, 0);
EXPECT_TRUE(prediction.isTaken);
EXPECT_EQ(prediction.target, 12);
}
} // namespace simeng

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