[cfe-commits] r92525 - in /cfe/trunk: lib/Sema/SemaExpr.cpp test/Sema/compare.c
John McCall
rjmccall at apple.com
Mon Jan 4 14:35:07 PST 2010
Author: rjmccall
Date: Mon Jan 4 16:35:07 2010
New Revision: 92525
URL: http://llvm.org/viewvc/llvm-project?rev=92525&view=rev
Log:
-Wsign-compare shouldn't warn when the signed operand is a conditional operator
whose operands are non-negative integer constant expressions. This comes up
in LLVM in a few places.
Modified:
cfe/trunk/lib/Sema/SemaExpr.cpp
cfe/trunk/test/Sema/compare.c
Modified: cfe/trunk/lib/Sema/SemaExpr.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaExpr.cpp?rev=92525&r1=92524&r2=92525&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaExpr.cpp (original)
+++ cfe/trunk/lib/Sema/SemaExpr.cpp Mon Jan 4 16:35:07 2010
@@ -5110,6 +5110,22 @@
return LHSTy;
}
+/// Returns true if we can prove that the result of the given
+/// integral expression will not have its sign bit set.
+static bool IsSignBitProvablyZero(ASTContext &Context, Expr *E) {
+ E = E->IgnoreParens();
+
+ llvm::APSInt value;
+ if (E->isIntegerConstantExpr(value, Context))
+ return value.isNonNegative();
+
+ if (ConditionalOperator *CO = dyn_cast<ConditionalOperator>(E))
+ return IsSignBitProvablyZero(Context, CO->getLHS()) &&
+ IsSignBitProvablyZero(Context, CO->getRHS());
+
+ return false;
+}
+
/// \brief Implements -Wsign-compare.
///
/// \param lex the left-hand expression
@@ -5157,27 +5173,15 @@
// If the value is a non-negative integer constant, then the
// signed->unsigned conversion won't change it.
- llvm::APSInt value;
- if (signedOperand->isIntegerConstantExpr(value, Context)) {
- assert(value.isSigned() && "result of signed expression not signed");
-
- if (value.isNonNegative())
- return;
- }
+ if (IsSignBitProvablyZero(Context, signedOperand))
+ return;
- if (Equality) {
- // For (in)equality comparisons, if the unsigned operand is a
- // constant which cannot collide with a overflowed signed operand,
- // then reinterpreting the signed operand as unsigned will not
- // change the result of the comparison.
- if (unsignedOperand->isIntegerConstantExpr(value, Context)) {
- assert(!value.isSigned() && "result of unsigned expression is signed");
-
- // 2's complement: test the top bit.
- if (value.isNonNegative())
- return;
- }
- }
+ // For (in)equality comparisons, if the unsigned operand is a
+ // constant which cannot collide with a overflowed signed operand,
+ // then reinterpreting the signed operand as unsigned will not
+ // change the result of the comparison.
+ if (Equality && IsSignBitProvablyZero(Context, unsignedOperand))
+ return;
Diag(OpLoc, PD)
<< lex->getType() << rex->getType()
Modified: cfe/trunk/test/Sema/compare.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/compare.c?rev=92525&r1=92524&r2=92525&view=diff
==============================================================================
--- cfe/trunk/test/Sema/compare.c (original)
+++ cfe/trunk/test/Sema/compare.c Mon Jan 4 16:35:07 2010
@@ -194,6 +194,9 @@
((short) a < (unsigned short) 0x80000) + // expected-warning {{comparison of integers of different signs}}
((signed char) a < (unsigned char) 0x80000) + // expected-warning {{comparison of integers of different signs}}
+ // We should be able to avoid warning about this.
+ (b != (a < 4 ? 1 : 2)) +
+
10
;
}
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