From 28a024ac4a5f22ce0fe31b0c0832989c6e9b0492 Mon Sep 17 00:00:00 2001
From: chrchr-github <78114321+chrchr-github@users.noreply.github.com>
Date: Mon, 11 Apr 2022 20:42:54 +0200
Subject: [PATCH] Fix #9954 incorrectLogicOperator/knownConditionTrueFalse for
 constexpr (#4002)

---
 lib/checkcondition.cpp | 18 ++++++++++++++----
 test/testcondition.cpp |  9 +++++++++
 2 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/lib/checkcondition.cpp b/lib/checkcondition.cpp
index 9a3dd7483..60dcc1e05 100644
--- a/lib/checkcondition.cpp
+++ b/lib/checkcondition.cpp
@@ -1025,6 +1025,11 @@ static std::string conditionString(const Token * tok)
     return tok->expressionString();
 }
 
+static bool isIfConstexpr(const Token* tok) {
+    const Token* const top = tok->astTop();
+    return top && Token::simpleMatch(top->astOperand1(), "if") && top->astOperand1()->isConstexpr();
+}
+
 void CheckCondition::checkIncorrectLogicOperator()
 {
     const bool printStyle = mSettings->severity.isEnabled(Severity::style);
@@ -1144,10 +1149,12 @@ void CheckCondition::checkIncorrectLogicOperator()
             ErrorPath errorPath;
 
             // Opposite comparisons around || or && => always true or always false
-            if (!isfloat && isOppositeCond(tok->str() == "||", mTokenizer->isCPP(), tok->astOperand1(), tok->astOperand2(), mSettings->library, true, true, &errorPath)) {
-
-                const bool alwaysTrue(tok->str() == "||");
-                incorrectLogicOperatorError(tok, conditionString(tok), alwaysTrue, inconclusive, errorPath);
+            const bool isLogicalOr(tok->str() == "||");
+            if (!isfloat && isOppositeCond(isLogicalOr, mTokenizer->isCPP(), tok->astOperand1(), tok->astOperand2(), mSettings->library, true, true, &errorPath)) {
+                if (!isIfConstexpr(tok)) {
+                    const bool alwaysTrue(isLogicalOr);
+                    incorrectLogicOperatorError(tok, conditionString(tok), alwaysTrue, inconclusive, errorPath);
+                }
                 continue;
             }
 
@@ -1494,6 +1501,9 @@ void CheckCondition::alwaysTrueFalse()
             if (hasSizeof)
                 continue;
 
+            if (isIfConstexpr(tok))
+                continue;
+
             alwaysTrueFalseError(tok, &tok->values().front());
         }
     }
diff --git a/test/testcondition.cpp b/test/testcondition.cpp
index 4c5c28fad..a94a505dc 100644
--- a/test/testcondition.cpp
+++ b/test/testcondition.cpp
@@ -3438,6 +3438,15 @@ private:
               "}");
         ASSERT_EQUALS("", errout.str());
 
+        // #9954
+        check("void f() {\n"
+              "    const size_t a(8 * sizeof(short));\n"
+              "    const size_t b(8 * sizeof(int));\n"
+              "    if constexpr (a == 16 && b == 16) {}\n"
+              "    else if constexpr (a == 16 && b == 32) {}\n"
+              "}\n");
+        ASSERT_EQUALS("", errout.str());
+
         // #9319
         check("struct S {\n"
               "  int a;\n"