Use a std::unordered_map for looking up sections by name (#1357)

include/asm/section.hpp

@@ -5,6 +5,8 @@
 
 #include <deque>
 #include <stdint.h>
+#include <string>
+#include <unordered_map>
 #include <vector>
 
 #include "linkdefs.hpp"
@@ -49,6 +51,7 @@ struct SectionSpec {
 };
 
 extern std::deque<Section> sectionList;
+extern std::unordered_map<std::string, size_t> sectionMap; // Indexes into `sectionList`
 extern Section *currentSection;
 
 Section *sect_FindSectionByName(char const *name);

src/asm/output.cpp

@@ -83,10 +83,8 @@ static uint32_t getSectIDIfAny(Section *sect) {
 	if (!sect)
 		return (uint32_t)-1;
 
-	for (auto it = sectionList.begin(); it != sectionList.end(); it++) {
-		if (&*it == sect)
-			return it - sectionList.begin();
-	}
+	if (auto search = sectionMap.find(sect->name); search != sectionMap.end())
+		return (uint32_t)(sectionMap.size() - search->second - 1);
 
 	fatalerror("Unknown section '%s'\n", sect->name.c_str());
 }
@@ -373,8 +371,8 @@ void out_WriteObject() {
 	for (Symbol const *sym : objectSymbols)
 		writesymbol(*sym, f);
 
-	for (Section &sect : sectionList)
-		writesection(sect, f);
+	for (auto it = sectionList.rbegin(); it != sectionList.rend(); it++)
+		writesection(*it, f);
 
 	putlong(assertions.size(), f);
 

src/asm/section.cpp

@@ -11,7 +11,6 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <string>
 
 #include "error.hpp"
 
@@ -41,6 +40,7 @@ struct SectionStackEntry {
 std::stack<UnionStackEntry> currentUnionStack;
 std::deque<SectionStackEntry> sectionStack;
 std::deque<Section> sectionList;
+std::unordered_map<std::string, size_t> sectionMap; // Indexes into `sectionList`
 uint32_t curOffset; // Offset into the current section (see sect_GetSymbolOffset)
 Section *currentSection = nullptr;
 static Section *currentLoadSection = nullptr;
@@ -110,11 +110,8 @@ attr_(warn_unused_result) static bool reserveSpace(uint32_t delta_size) {
 }
 
 Section *sect_FindSectionByName(char const *name) {
-	for (Section &sect : sectionList) {
-		if (sect.name == name)
-			return &sect;
-	}
-	return nullptr;
+	auto search = sectionMap.find(name);
+	return search != sectionMap.end() ? &sectionList[search->second] : nullptr;
 }
 
 #define mask(align) ((1U << (align)) - 1)
@@ -300,8 +297,9 @@ static Section *createSection(
     uint16_t alignOffset,
     SectionModifier mod
 ) {
-	// Add the new section to the list (order doesn't matter)
-	Section &sect = sectionList.emplace_front();
+	// Add the new section to the list
+	Section &sect = sectionList.emplace_back();
+	sectionMap.emplace(name, sectionMap.size());
 
 	sect.name = name;
 	sect.type = type;