Add a new subgroup to -Wtautological-compare, -Wtautological-overlap-compare,
which warns on compound conditionals that always evaluate to the same value.
For instance, (x > 5 && x < 3) will always be false since no value for x can
satisfy both conditions.
This patch also changes the CFG to use these tautological values for better
branch analysis. The test for -Wunreachable-code shows how this change catches
additional dead code.
Patch by Anders Rönnholm.
llvm-svn: 205665
diff --git a/clang/test/Sema/warn-overlap.c b/clang/test/Sema/warn-overlap.c
new file mode 100644
index 0000000..c985471
--- /dev/null
+++ b/clang/test/Sema/warn-overlap.c
@@ -0,0 +1,58 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -Wtautological-overlap-compare %s
+
+#define mydefine 2
+
+void f(int x) {
+ int y = 0;
+
+ // > || <
+ if (x > 2 || x < 1) { }
+ if (x > 2 || x < 2) { }
+ if (x != 2 || x != 3) { } // expected-warning {{overlapping comparisons always evaluate to true}}
+ if (x > 2 || x < 3) { } // expected-warning {{overlapping comparisons always evaluate to true}}
+ if (x > 0 || x < 0) { }
+
+ if (x > 2 || x <= 1) { }
+ if (x > 2 || x <= 2) { } // expected-warning {{overlapping comparisons always evaluate to true}}
+ if (x > 2 || x <= 3) { } // expected-warning {{overlapping comparisons always evaluate to true}}
+
+ if (x >= 2 || x < 1) { }
+ if (x >= 2 || x < 2) { } // expected-warning {{overlapping comparisons always evaluate to true}}
+ if (x >= 2 || x < 3) { } // expected-warning {{overlapping comparisons always evaluate to true}}
+
+ if (x >= 2 || x <= 1) { } // expected-warning {{overlapping comparisons always evaluate to true}}
+ if (x >= 2 || x <= 2) { } // expected-warning {{overlapping comparisons always evaluate to true}}
+ if (x >= 2 || x <= 3) { } // expected-warning {{overlapping comparisons always evaluate to true}}
+ if (x >= 0 || x <= 0) { } // expected-warning {{overlapping comparisons always evaluate to true}}
+
+ // > && <
+ if (x > 2 && x < 1) { } // expected-warning {{overlapping comparisons always evaluate to false}}
+ if (x > 2 && x < 2) { } // expected-warning {{overlapping comparisons always evaluate to false}}
+ if (x > 2 && x < 3) { } // expected-warning {{overlapping comparisons always evaluate to false}}
+ if (x > 0 && x < 1) { } // expected-warning {{overlapping comparisons always evaluate to false}}
+
+ if (x > 2 && x <= 1) { } // expected-warning {{overlapping comparisons always evaluate to false}}
+ if (x > 2 && x <= 2) { } // expected-warning {{overlapping comparisons always evaluate to false}}
+ if (x > 2 && x <= 3) { }
+
+ if (x >= 2 && x < 1) { } // expected-warning {{overlapping comparisons always evaluate to false}}
+ if (x >= 2 && x < 2) { } // expected-warning {{overlapping comparisons always evaluate to false}}
+ if (x >= 2 && x < 3) { }
+ if (x >= 0 && x < 0) { } // expected-warning {{overlapping comparisons always evaluate to false}}
+
+ if (x >= 2 && x <= 1) { } // expected-warning {{overlapping comparisons always evaluate to false}}
+ if (x >= 2 && x <= 2) { }
+ if (x >= 2 && x <= 3) { }
+
+ // !=, ==, ..
+ if (x != 2 || x != 3) { } // expected-warning {{overlapping comparisons always evaluate to true}}
+ if (x != 2 || x < 3) { } // expected-warning {{overlapping comparisons always evaluate to true}}
+ if (x == 2 && x == 3) { } // expected-warning {{overlapping comparisons always evaluate to false}}
+ if (x == 2 && x > 3) { } // expected-warning {{overlapping comparisons always evaluate to false}}
+ if (x == 3 && x < 0) { } // expected-warning {{overlapping comparisons always evaluate to false}}
+ if (3 == x && x < 0) { } // expected-warning {{overlapping comparisons always evaluate to false}}
+
+ if (x == mydefine && x > 3) { }
+ if (x == (mydefine + 1) && x > 3) { }
+}
+
