From 380277e46ec1d2d9abedcddf357ceea935cbe576 Mon Sep 17 00:00:00 2001 From: Ted Kremenek Date: Wed, 15 Oct 2008 05:23:41 +0000 Subject: [PATCH] Enhance dead store checker to not flag preincrements to dead variables where the preincrement is a subexpression, e.g. foo(++x); This can cause false negatives, but will remove a whole class of false positives. git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@57554 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Analysis/CheckDeadStores.cpp | 7 +++++++ test/Analysis/dead-stores.c | 8 +++++++- 2 files changed, 14 insertions(+), 1 deletion(-) diff --git a/lib/Analysis/CheckDeadStores.cpp b/lib/Analysis/CheckDeadStores.cpp index d87bfb1964..2afc7e0235 100644 --- a/lib/Analysis/CheckDeadStores.cpp +++ b/lib/Analysis/CheckDeadStores.cpp @@ -149,6 +149,13 @@ public: else if (UnaryOperator* U = dyn_cast(S)) { if (!U->isIncrementOp()) return; + + // Handle: ++x within a subexpression. The solution is not warn + // about preincrements to dead variables when the preincrement occurs + // as a subexpression. This can lead to false negatives, e.g. "(++x);" + // A generalized dead code checker should find such issues. + if (U->isPrefix() && Parents.isSubExpr(U)) + return; Expr *Ex = U->getSubExpr()->IgnoreParenCasts(); diff --git a/test/Analysis/dead-stores.c b/test/Analysis/dead-stores.c index 2a67afd0b0..71c4e3b28b 100644 --- a/test/Analysis/dead-stores.c +++ b/test/Analysis/dead-stores.c @@ -74,9 +74,15 @@ int f10() { int f11() { int x = 4; - return ++x; // expected-warning{{never read}} + return x++; // expected-warning{{never read}} } +int f11b() { + int x = 4; + return ++x; // no-warning +} + + int f12a(int y) { int x = y; // expected-warning{{never read}} return 1; -- 2.40.0