From: Douglas Gregor <dgregor@apple.com>
Date: Mon, 1 Mar 2010 01:04:55 +0000 (+0000)
Subject: Don't warn about case-value conversions from a negative value to a
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=f9f627dbbc62fbf51b906c24c783b4249dc7e9bb;p=clang

Don't warn about case-value conversions from a negative value to a
larger unsigned value, since this is implementation-defined
behavior. (We previously suppressed this warning when converting from
a signed value to an unsigned value of the same size).


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@97430 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Sema/SemaStmt.cpp b/lib/Sema/SemaStmt.cpp
index bdd0962a11..540189cd83 100644
--- a/lib/Sema/SemaStmt.cpp
+++ b/lib/Sema/SemaStmt.cpp
@@ -314,15 +314,13 @@ void Sema::ConvertIntegerToTypeWarnOnOverflow(llvm::APSInt &Val,
   // Perform a conversion to the promoted condition type if needed.
   if (NewWidth > Val.getBitWidth()) {
     // If this is an extension, just do it.
-    llvm::APSInt OldVal(Val);
     Val.extend(NewWidth);
-
-    // If the input was signed and negative and the output is unsigned,
-    // warn.
-    if (!NewSign && OldVal.isSigned() && OldVal.isNegative())
-      Diag(Loc, DiagID) << OldVal.toString(10) << Val.toString(10);
-
     Val.setIsSigned(NewSign);
+
+    // If the input was signed and negative and the output is
+    // unsigned, don't bother to warn: this is implementation-defined
+    // behavior.
+    // FIXME: Introduce a second, default-ignored warning for this case?
   } else if (NewWidth < Val.getBitWidth()) {
     // If this is a truncation, check for overflow.
     llvm::APSInt ConvVal(Val);
diff --git a/test/Sema/switch.c b/test/Sema/switch.c
index 213cd0a75b..e63a1942bb 100644
--- a/test/Sema/switch.c
+++ b/test/Sema/switch.c
@@ -254,3 +254,10 @@ int test14(int a) {
   }
   return 0;
 }
+
+void f1(unsigned x) {
+  switch (x) {
+  case -1: break;
+  default: break;
+  }
+}