Branch Predictor

Signed-off-by: Gaurav Kukreja <gaurav@gauravk.in>

branch_predictor/.cproject

+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<?fileVersion 4.0.0?><cproject storage_type_id="org.eclipse.cdt.core.XmlProjectDescriptionStorage">
+	<storageModule moduleId="org.eclipse.cdt.core.settings">
+		<cconfiguration id="cdt.managedbuild.toolchain.gnu.base.992304088">
+			<storageModule buildSystemId="org.eclipse.cdt.managedbuilder.core.configurationDataProvider" id="cdt.managedbuild.toolchain.gnu.base.992304088" moduleId="org.eclipse.cdt.core.settings" name="Default">
+				<externalSettings/>
+				<extensions>
+					<extension id="org.eclipse.cdt.core.GmakeErrorParser" point="org.eclipse.cdt.core.ErrorParser"/>
+					<extension id="org.eclipse.cdt.core.CWDLocator" point="org.eclipse.cdt.core.ErrorParser"/>
+					<extension id="org.eclipse.cdt.core.GCCErrorParser" point="org.eclipse.cdt.core.ErrorParser"/>
+					<extension id="org.eclipse.cdt.core.GASErrorParser" point="org.eclipse.cdt.core.ErrorParser"/>
+					<extension id="org.eclipse.cdt.core.GLDErrorParser" point="org.eclipse.cdt.core.ErrorParser"/>
+					<extension id="org.eclipse.cdt.core.ELF" point="org.eclipse.cdt.core.BinaryParser"/>
+				</extensions>
+			</storageModule>
+			<storageModule moduleId="cdtBuildSystem" version="4.0.0">
+				<configuration buildProperties="" id="cdt.managedbuild.toolchain.gnu.base.992304088" name="Default" parent="org.eclipse.cdt.build.core.emptycfg">
+					<folderInfo id="cdt.managedbuild.toolchain.gnu.base.992304088.348474428" name="/" resourcePath="">
+						<toolChain id="cdt.managedbuild.toolchain.gnu.base.562303481" name="cdt.managedbuild.toolchain.gnu.base" superClass="cdt.managedbuild.toolchain.gnu.base">
+							<targetPlatform archList="all" binaryParser="org.eclipse.cdt.core.ELF" id="cdt.managedbuild.target.gnu.platform.base.1601399728" name="Debug Platform" osList="linux,hpux,aix,qnx" superClass="cdt.managedbuild.target.gnu.platform.base"/>
+							<builder id="cdt.managedbuild.target.gnu.builder.base.1508323901" managedBuildOn="false" name="Gnu Make Builder.Default" superClass="cdt.managedbuild.target.gnu.builder.base"/>
+							<tool id="cdt.managedbuild.tool.gnu.archiver.base.1136083684" name="GCC Archiver" superClass="cdt.managedbuild.tool.gnu.archiver.base"/>
+							<tool id="cdt.managedbuild.tool.gnu.cpp.compiler.base.1052829016" name="GCC C++ Compiler" superClass="cdt.managedbuild.tool.gnu.cpp.compiler.base"/>
+							<tool id="cdt.managedbuild.tool.gnu.c.compiler.base.863213174" name="GCC C Compiler" superClass="cdt.managedbuild.tool.gnu.c.compiler.base"/>
+							<tool id="cdt.managedbuild.tool.gnu.c.linker.base.2031525796" name="GCC C Linker" superClass="cdt.managedbuild.tool.gnu.c.linker.base"/>
+							<tool id="cdt.managedbuild.tool.gnu.cpp.linker.base.314488841" name="GCC C++ Linker" superClass="cdt.managedbuild.tool.gnu.cpp.linker.base"/>
+							<tool id="cdt.managedbuild.tool.gnu.assembler.base.897217205" name="GCC Assembler" superClass="cdt.managedbuild.tool.gnu.assembler.base"/>
+						</toolChain>
+					</folderInfo>
+				</configuration>
+			</storageModule>
+			<storageModule moduleId="org.eclipse.cdt.core.externalSettings"/>
+		</cconfiguration>
+	</storageModule>
+	<storageModule moduleId="cdtBuildSystem" version="4.0.0">
+		<project id="branch_predictor.null.1371780544" name="branch_predictor"/>
+	</storageModule>
+	<storageModule moduleId="scannerConfiguration">
+		<autodiscovery enabled="true" problemReportingEnabled="true" selectedProfileId=""/>
+	</storageModule>
+	<storageModule moduleId="org.eclipse.cdt.core.LanguageSettingsProviders"/>
+</cproject>

branch_predictor/.project

+<?xml version="1.0" encoding="UTF-8"?>
+<projectDescription>
+	<name>branch_predictor</name>
+	<comment></comment>
+	<projects>
+	</projects>
+	<buildSpec>
+		<buildCommand>
+			<name>org.eclipse.cdt.managedbuilder.core.genmakebuilder</name>
+			<triggers>clean,full,incremental,</triggers>
+			<arguments>
+			</arguments>
+		</buildCommand>
+		<buildCommand>
+			<name>org.eclipse.cdt.managedbuilder.core.ScannerConfigBuilder</name>
+			<triggers>full,incremental,</triggers>
+			<arguments>
+			</arguments>
+		</buildCommand>
+	</buildSpec>
+	<natures>
+		<nature>org.eclipse.cdt.core.cnature</nature>
+		<nature>org.eclipse.cdt.managedbuilder.core.managedBuildNature</nature>
+		<nature>org.eclipse.cdt.managedbuilder.core.ScannerConfigNature</nature>
+	</natures>
+</projectDescription>

branch_predictor/Makefile

+# Makefile for cache simulator
+include Makefile.macros
+
+SRC = $(BPRED_SRC)
+LIB = $(BPRED_LIB)
+
+INSTALL = cp
+
+all: branchPred
+
+branchPred: 
+	$(MAKE) -C $(SRC)
+	$(INSTALL) $(SRC)/lib$@.so $(LIB)
+	
+clean:
+	rm -rf *.o
+	rm -rf $(LIB)/libbranchPred.so

branch_predictor/Makefile.macros

+# Configuration for cache simulator
+
+# Stupid Makefile Issue: Make sure no white space at the end of the variable declarations
+
+# http://stackoverflow.com/questions/18136918/how-to-get-current-directory-of-your-makefile
+mkfile_path := $(abspath $(lastword $(MAKEFILE_LIST)))
+current_dir := $(patsubst %/,%,$(dir $(mkfile_path)))
+
+# Path to Cache Simulator
+BPRED_DIR := $(current_dir)
+
+BPRED_SRC = $(BPRED_DIR)/src
+BPRED_HEADERS = $(BPRED_DIR)/headers/
+BPRED_LIB = $(BPRED_DIR)/lib/

branch_predictor/headers/branchPred.h

+/**
+ * Called when a new branch is entered.
+ *
+ * name: string containing name of the basic block.
+ * blockObjStartAdd : Starting address of basic block from objdump
+ * blockObjEndAdd : End address of basic block from objdump
+ *
+ * returns whether branch was predicted or not
+ */
+extern unsigned int enterBlock (unsigned long blockObjStartAdd,
+		unsigned long blockObjEndAdd);
+
+
+extern void branchPred_init();

branch_predictor/src/Makefile

+include ../Makefile.macros
+
+GCC = gcc
+CFLAGS = -O3
+
+HEADERS = $(BPRED_HEADERS)
+
+# Cache Simulation Source Code
+SOURCES = branchPred.c $(HEADERS)/branchPred.h
+OBJECTS = branchPred.o
+
+all: branchPred
+
+branchPred: $(SOURCES)
+	$(GCC) $(CFLAGS) -c -Wall -Werror -fpic $^
+	$(GCC) -shared -o lib$@.so $(OBJECTS)
+	
+clean:
+	rm -rf *.o libbranchPred.so
\ No newline at end of file

branch_predictor/src/branchPred.c

+#include <stdio.h>
+#include <stdlib.h>
+
+#define BPRED_TABLE_MAX_ENTRIES 125
+
+enum predictionValues {
+	UNKNOWN = -1,
+	STRONGLY_TAKEN = 0,
+	WEAKLY_TAKEN,
+	WEAKLY_NOT_TAKEN,
+	STRONGLY_NOT_TAKEN
+};
+typedef enum predictionValues prediction_t;
+
+struct bPredTableEntry
+{
+	unsigned long branchInstAdd;
+	prediction_t prediction;
+	struct bPredTableEntry *next;
+	struct bPredTableEntry *prev;
+};
+typedef struct bPredTableEntry bPredTableEntry_t;
+
+bPredTableEntry_t *bPredTable_head;
+bPredTableEntry_t *bPredTable_tail;
+unsigned int bPredTableEntries;
+
+unsigned int prevBlockValid;
+unsigned long prevBlockEndAdd;
+
+void removeHeadEntry()
+{
+	// bPredTable_head and the next pointer must not be NULL
+	// TODO: Add an assert!
+	bPredTableEntry_t *tmp;
+	tmp = bPredTable_head;
+	bPredTable_head = bPredTable_head->next;
+	bPredTable_head->prev = NULL;
+	free(tmp);
+}
+
+void insertEntryToTail(bPredTableEntry_t *entry)
+{
+	if (bPredTableEntries == BPRED_TABLE_MAX_ENTRIES)
+	{
+		// Table Capacity full, must remove least recently used to make space
+
+	}
+	if (bPredTable_head == NULL &&
+			bPredTable_tail == NULL)
+	{
+		entry->next = NULL;
+		entry->prev = NULL;
+		bPredTable_head = entry;
+		bPredTable_tail = entry;
+		return;
+	}
+	else
+	{
+		bPredTable_tail->next = entry;
+		entry->prev = bPredTable_tail;
+		entry->next = NULL;
+		bPredTable_tail = entry;
+		return;
+	}
+}
+
+void moveEntryToTail(bPredTableEntry_t *entry)
+{
+	if (entry->next == NULL)
+		return; // already at tail
+	else if (entry->prev == NULL) {
+		// Entry is head
+		bPredTable_head = entry->next;
+		bPredTable_head->prev = NULL;
+		bPredTable_tail->next = entry;
+		entry->prev = bPredTable_tail;
+		entry->next = NULL;
+		bPredTable_tail = entry;
+		return;
+	}
+	else
+	{
+		entry->prev->next = entry->next;
+		entry->next->prev = entry->prev;
+		bPredTable_tail->next = entry;
+		entry->prev = bPredTable_tail;
+		entry->next = NULL;
+		bPredTable_tail = entry;
+		return;
+	}
+}
+
+/**
+ * Called when a new branch is entered.
+ *
+ * name: string containing name of the basic block.
+ * blockObjStartAdd : Starting address of basic block from objdump
+ * blockObjEndAdd : End address of basic block from objdump
+ *
+ * returns whether branch was predicted or not
+ */
+unsigned int enterBlock (unsigned long blockObjStartAdd,
+		unsigned long blockObjEndAdd)
+{
+	int isBranchTaken;
+	int predicted = -1;
+
+	if (!prevBlockValid)
+	{
+		// No Previous block, so branch not predicted!
+		// Set current block as previous
+		prevBlockValid = 1;
+		prevBlockEndAdd = blockObjEndAdd;
+		predicted =  0;
+	}
+
+	if (blockObjStartAdd == prevBlockEndAdd + 4)
+	{
+		// Branch was not taken!
+		isBranchTaken = 0;
+	}
+	else
+	{
+		// Branch was taken!
+		isBranchTaken = 1;
+	}
+
+	bPredTableEntry_t *entry = bPredTable_tail;
+	while(entry != NULL)
+	{
+		if (entry->branchInstAdd == prevBlockEndAdd)
+		{
+			// Entry Found!
+			if (entry->prediction == STRONGLY_NOT_TAKEN)
+			{
+				if (isBranchTaken)
+				{
+					entry->prediction = WEAKLY_NOT_TAKEN;
+					predicted =  0; // not predicted
+					break;
+				}
+				else
+				{
+					predicted =  1; // predicted
+					break;
+				}
+			}
+			if (entry->prediction == WEAKLY_NOT_TAKEN)
+			{
+				if (isBranchTaken)
+				{
+					entry->prediction = WEAKLY_TAKEN;
+					predicted =  0; // not predicted
+					break;
+				}
+				else
+				{
+					entry->prediction = STRONGLY_NOT_TAKEN;
+					predicted =  1; // predicted
+					break;
+				}
+			}
+			if (entry->prediction == WEAKLY_TAKEN)
+			{
+				if (isBranchTaken)
+				{
+					entry->prediction = STRONGLY_TAKEN;
+					predicted =  1; // predicted
+					break;
+				}
+				else
+				{
+					entry->prediction = WEAKLY_NOT_TAKEN;
+					predicted =  0; // not predicted
+					break;
+				}
+			}
+			if (entry->prediction == STRONGLY_TAKEN)
+			{
+				if (isBranchTaken)
+				{
+					predicted =  1; // predicted
+					break;
+				}
+				else
+				{
+					entry->prediction = WEAKLY_TAKEN;
+					predicted =  0; // not predicted
+					break;
+				}
+			}
+		}
+		entry = entry->prev;
+	}
+
+	if (entry != NULL)
+	{
+		// Entry was found!
+		moveEntryToTail(entry);
+	}
+	else
+	{
+		// Entry was not found!
+		entry = malloc(sizeof(bPredTableEntry_t));
+		entry->branchInstAdd = blockObjEndAdd;
+		if (isBranchTaken)
+		{
+			entry->prediction = WEAKLY_NOT_TAKEN;
+			predicted = 0;
+		}
+		else
+		{
+			entry->prediction = STRONGLY_NOT_TAKEN;
+			predicted = 1;
+		}
+		insertEntryToTail(entry);
+	}
+
+	prevBlockEndAdd = blockObjEndAdd;
+
+//	if (!predicted)
+//	{
+//		printf("Branch NOT Predicted\n");
+//	}
+
+	return predicted;
+}
+
+void branchPred_init() {
+	bPredTable_head = NULL;
+	bPredTable_tail = NULL;
+	bPredTableEntries = 0;
+	prevBlockValid = 0;
+}