From 1b500bb0d40aa3ebf1ace47340bb5f401a9ae99c Mon Sep 17 00:00:00 2001 From: Ted Kremenek Date: Thu, 29 Nov 2007 00:59:04 +0000 Subject: [PATCH] Enhanced implementation of -Wfloat-equal to check for comparisons against floating-point literals that are represented exactly by the APFloat in FloatingLiteral. For such literals, we do not emit a warning since such checks are often performed in real code to see if a variable has changed from its original value. This heuristic clearly can lead to false negatives, but the hope is it will significantly reduce false positives to help make the compiler flag more useful. git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@44424 91177308-0d34-0410-b5e6-96231b3b80d8 --- Sema/SemaChecking.cpp | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/Sema/SemaChecking.cpp b/Sema/SemaChecking.cpp index cb22f03a31..20f0b81b43 100644 --- a/Sema/SemaChecking.cpp +++ b/Sema/SemaChecking.cpp @@ -715,6 +715,24 @@ void Sema::CheckFloatComparison(SourceLocation loc, Expr* lex, Expr *rex) { if (DRL->getDecl() == DRR->getDecl()) EmitWarning = false; + + // Special case: check for comparisons against literals that can be exactly + // represented by APFloat. In such cases, do not emit a warning. This + // is a heuristic: often comparison against such literals are used to + // detect if a value in a variable has not changed. This clearly can + // lead to false negatives. + if (EmitWarning) { + if (FloatingLiteral* FLL = dyn_cast(LeftExprSansParen)) { + if (FLL->isExact()) + EmitWarning = false; + } + else + if (FloatingLiteral* FLR = dyn_cast(RightExprSansParen)){ + if (FLR->isExact()) + EmitWarning = false; + } + } + // Check for comparisons with builtin types. if (EmitWarning) if (CallExpr* CL = dyn_cast(LeftExprSansParen)) -- 2.40.0