Add optimization option --fcombine-load-threshold=XXX

include/config.h

@@ -105,6 +105,10 @@ namespace vc4c
          * Whether moving of constants to out side of loops
          */
         bool moveConstants = true;
+        /*
+         * The threshold for combineLoadingLiterals
+         */
+        int combineLoadingLiteralsThreshold = 6;
     };
 
     /*

src/main.cpp

@@ -101,6 +101,41 @@ static void printInfo()
     std::cout << vc4c::to_string<std::string>(infoString, "; ") << std::endl;
 }
 
+/*
+ * parse options with parameter like xxx=n
+ * if invalid parameter are passed, raise an exception
+ */
+Optional<int> parseIntOption(std::string name, std::string input)
+{
+    std::stringstream ss(input);
+    std::string buffer;
+    std::getline(ss, buffer, '=');
+    if(buffer == name)
+    {
+        // XXX if input doesn't include '=', `ss` already reached the end.
+        // Then, the second `std::getline` do nothing.
+        // To detect that checking `name` == `buffer` is required.
+        std::getline(ss, buffer, '=');
+        if(name == buffer)
+        {
+            std::string err = "option parse error: parameter of integer expected in " + name;
+            throw CompilationError(CompilationStep::PRECOMPILATION, err);
+        }
+        try
+        {
+            auto s = std::stoi(buffer);
+            return Optional<int>(s);
+        }
+        catch(const std::invalid_argument& e)
+        {
+            std::string err = "option parse error: parameter of integer expected in " + name + ", but " + buffer;
+            throw CompilationError(CompilationStep::PRECOMPILATION, err);
+        }
+    }
+
+    return {};
+}
+
 /*
  *
  */
@@ -178,9 +213,9 @@ int main(int argc, char** argv)
             config.frontend = Frontend::LLVM_IR;
         else if(strcmp("--disassemble", argv[i]) == 0)
             runDisassembler = true;
-        else if(strcmp("--fmoveconstants", argv[i]) == 0)
+        else if(strcmp("--fmove-constants", argv[i]) == 0)
             config.moveConstants = true;
-        else if(strcmp("--fnomoveconstants", argv[i]) == 0)
+        else if(strcmp("--fnomove-constants", argv[i]) == 0)
             config.moveConstants = false;
         else if(strcmp("-o", argv[i]) == 0)
         {
@@ -189,6 +224,10 @@ int main(int argc, char** argv)
             i += 2;
             break;
         }
+        else if(auto opt = parseIntOption("--fcombine-load-threshold", argv[i]))
+        {
+            config.combineLoadingLiteralsThreshold = opt.value();
+        }
         else
             options.append(argv[i]).append(" ");
     }

src/optimization/Combiner.cpp

@@ -588,10 +588,10 @@ static Optional<Literal> getSourceLiteral(InstructionWalker it)
     return {};
 }
 
-static bool canReplaceLiteralLoad(InstructionWalker it, const InstructionWalker start, const InstructionWalker match)
+static bool canReplaceLiteralLoad(InstructionWalker it, const InstructionWalker start, const InstructionWalker match,
+    std::size_t stepsLeft = ACCUMULATOR_THRESHOLD_HINT)
 {
-    std::size_t stepsLeft = ACCUMULATOR_THRESHOLD_HINT;
-    InstructionWalker pos = it;
+    InstructionWalker pos = it.copy();
     // check whether the instruction last loading the same literal is at most ACCUMULATOR_THRESHOLD_HINT instructions
     // before this one
     while(stepsLeft > 0 && !pos.isStartOfBlock() && pos != start)
@@ -620,7 +620,8 @@ void optimizations::combineLoadingLiterals(const Module& module, Method& method,
                 if(literal)
                 {
                     if(lastLoadImmediate.find(literal->unsignedInt()) != lastLoadImmediate.end() &&
-                        canReplaceLiteralLoad(it, block.begin(), lastLoadImmediate.at(literal->unsignedInt())))
+                        canReplaceLiteralLoad(it, block.begin(), lastLoadImmediate.at(literal->unsignedInt()),
+                            config.combineLoadingLiteralsThreshold))
                     {
                         Local* oldLocal = it->getOutput()->local;
                         Local* newLocal = lastLoadImmediate.at(literal->unsignedInt())->getOutput()->local;