Fix 10676: FP: Array index -1 is out of bounds. (#3670)

Makefile

@@ -411,7 +411,7 @@ validateRules:
 $(libcppdir)/analyzerinfo.o: lib/analyzerinfo.cpp externals/tinyxml2/tinyxml2.h lib/analyzerinfo.h lib/color.h lib/config.h lib/errorlogger.h lib/errortypes.h lib/importproject.h lib/path.h lib/platform.h lib/suppressions.h lib/utils.h
 	$(CXX) ${INCLUDE_FOR_LIB} $(CPPFLAGS) $(CPPFILESDIR) $(CXXFLAGS) $(UNDEF_STRICT_ANSI) -c -o $(libcppdir)/analyzerinfo.o $(libcppdir)/analyzerinfo.cpp
 
-$(libcppdir)/astutils.o: lib/astutils.cpp lib/astutils.h lib/config.h lib/errortypes.h lib/importproject.h lib/library.h lib/mathlib.h lib/platform.h lib/settings.h lib/standards.h lib/suppressions.h lib/symboldatabase.h lib/templatesimplifier.h lib/timer.h lib/token.h lib/utils.h lib/valueflow.h
+$(libcppdir)/astutils.o: lib/astutils.cpp lib/astutils.h lib/config.h lib/errortypes.h lib/importproject.h lib/infer.h lib/library.h lib/mathlib.h lib/platform.h lib/settings.h lib/standards.h lib/suppressions.h lib/symboldatabase.h lib/templatesimplifier.h lib/timer.h lib/token.h lib/utils.h lib/valueflow.h lib/valueptr.h
 	$(CXX) ${INCLUDE_FOR_LIB} $(CPPFLAGS) $(CPPFILESDIR) $(CXXFLAGS) $(UNDEF_STRICT_ANSI) -c -o $(libcppdir)/astutils.o $(libcppdir)/astutils.cpp
 
 $(libcppdir)/bughuntingchecks.o: lib/bughuntingchecks.cpp lib/astutils.h lib/bughuntingchecks.h lib/color.h lib/config.h lib/errorlogger.h lib/errortypes.h lib/exprengine.h lib/importproject.h lib/library.h lib/mathlib.h lib/platform.h lib/settings.h lib/standards.h lib/suppressions.h lib/symboldatabase.h lib/templatesimplifier.h lib/timer.h lib/token.h lib/utils.h lib/valueflow.h

lib/astutils.cpp

@@ -22,12 +22,14 @@
 
 #include "config.h"
 #include "errortypes.h"
+#include "infer.h"
 #include "library.h"
 #include "mathlib.h"
 #include "settings.h"
 #include "symboldatabase.h"
 #include "token.h"
 #include "valueflow.h"
+#include "valueptr.h"
 
 #include <algorithm>
 #include <functional>
@@ -687,9 +689,10 @@ bool extractForLoopValues(const Token *forToken,
     const Token *incExpr  = forToken->next()->astOperand2()->astOperand2()->astOperand2();
     if (!initExpr || !initExpr->isBinaryOp() || initExpr->str() != "=" || !Token::Match(initExpr->astOperand1(), "%var%"))
         return false;
+    std::vector<MathLib::bigint> minInitValue = getMinValue(makeIntegralInferModel(), initExpr->astOperand2()->values());
     *varid = initExpr->astOperand1()->varId();
     *knownInitValue = initExpr->astOperand2()->hasKnownIntValue();
-    *initValue = (*knownInitValue) ? initExpr->astOperand2()->getKnownIntValue() : 0;
+    *initValue = minInitValue.empty() ? 0 : minInitValue.front();
     *partialCond = Token::Match(condExpr, "%oror%|&&");
     visitAstNodes(condExpr, [varid, &condExpr](const Token *tok) {
         if (Token::Match(tok, "%oror%|&&"))

lib/infer.cpp

@@ -360,3 +360,16 @@ std::vector<ValueFlow::Value> infer(const ValuePtr<InferModel>& model,
 {
     return infer(model, op, std::move(lhsValues), {model->yield(rhs)});
 }
+
+std::vector<MathLib::bigint> getMinValue(const ValuePtr<InferModel>& model, const std::list<ValueFlow::Value>& values)
+{
+    return Interval::fromValues(values, [&](const ValueFlow::Value& v) {
+        return model->match(v);
+    }).minvalue;
+}
+std::vector<MathLib::bigint> getMaxValue(const ValuePtr<InferModel>& model, const std::list<ValueFlow::Value>& values)
+{
+    return Interval::fromValues(values, [&](const ValueFlow::Value& v) {
+        return model->match(v);
+    }).maxvalue;
+}

lib/infer.h

@@ -47,6 +47,9 @@ std::vector<ValueFlow::Value> infer(const ValuePtr<InferModel>& model,
                                     std::list<ValueFlow::Value> lhsValues,
                                     MathLib::bigint rhs);
 
+std::vector<MathLib::bigint> getMinValue(const ValuePtr<InferModel>& model, const std::list<ValueFlow::Value>& values);
+std::vector<MathLib::bigint> getMaxValue(const ValuePtr<InferModel>& model, const std::list<ValueFlow::Value>& values);
+
 std::string toString(const Interval& i);
 
 #endif

test/teststl.cpp

@@ -2057,6 +2057,19 @@ private:
               "        return a[4 - x];\n"
               "}");
         ASSERT_EQUALS("", errout.str());
+
+        check("std::array<int,6> values;\n"
+              "int get_value();\n"
+              "int compute() {\n"
+              "    int i = get_value();\n"
+              "    if( i < 0 || i > 5)\n"
+              "        return -1;\n"
+              "    int sum = 0;\n"
+              "    for( int j = i+1; j < 7; ++j)\n"
+              "        sum += values[j-1];\n"
+              "    return sum;\n"
+              "}\n");
+        ASSERT_EQUALS("", errout.str());
     }