On Tue, Nov 13, 2012 at 1:50 PM, Eli Friedman <[email protected]>wrote:
> On Tue, Nov 13, 2012 at 1:35 PM, Richard Trieu <[email protected]> wrote: > > On Mon, Nov 12, 2012 at 6:35 PM, Eli Friedman <[email protected]> > > wrote: > >> > >> On Mon, Nov 12, 2012 at 5:31 PM, Richard Trieu <[email protected]> > wrote: > >> > I uploaded a new patch. > >> > > >> > On Mon, Nov 12, 2012 at 11:22 AM, Eli Friedman < > [email protected]> > >> > wrote: > >> >> > >> >> Comments below. > >> >> > >> >> On Mon, Nov 12, 2012 at 9:46 AM, Richard Trieu <[email protected]> > >> >> wrote: > >> >> > Make -Wtautological-constant-out-of-range-compare checking take > into > >> >> > account types and conversion between types. The old version merely > >> >> > checked > >> >> > the bit widths, which allowed failed to catch a few cases, while > >> >> > warning on > >> >> > other safe comparisons. > >> >> > > >> >> > http://llvm-reviews.chandlerc.com/D113 > >> >> > > >> >> > Files: > >> >> > test/Analysis/additive-folding.cpp > >> >> > test/SemaCXX/compare.cpp > >> >> > test/SemaCXX/warn-enum-compare.cpp > >> >> > lib/Sema/SemaChecking.cpp > >> >> > >> >> Index: test/SemaCXX/warn-enum-compare.cpp > >> >> =================================================================== > >> >> --- test/SemaCXX/warn-enum-compare.cpp > >> >> +++ test/SemaCXX/warn-enum-compare.cpp > >> >> @@ -39,8 +39,8 @@ > >> >> while (b == c); > >> >> while (B1 == name1::B2); > >> >> while (B2 == name2::B1); > >> >> - while (x == AnonAA); // expected-warning {{comparison of constant > >> >> 42 with expression of type 'Foo' is always false}} > >> >> - while (AnonBB == y); // expected-warning {{comparison of constant > >> >> 45 with expression of type 'Bar' is always false}} > >> >> + while (x == AnonAA); > >> >> + while (AnonBB == y); > >> >> while (AnonAA == AnonAB); > >> >> while (AnonAB == AnonBA); > >> >> while (AnonBB == AnonAA); > >> >> > >> >> Why are you changing this warning? > >> > > >> > See discussion below at IntRange. > >> >> > >> >> > >> >> while (AnonBB == AnonAA); > >> >> Index: lib/Sema/SemaChecking.cpp > >> >> =================================================================== > >> >> --- lib/Sema/SemaChecking.cpp > >> >> +++ lib/Sema/SemaChecking.cpp > >> >> @@ -4328,38 +4328,91 @@ > >> >> Expr *Constant, Expr > *Other, > >> >> llvm::APSInt Value, > >> >> bool RhsConstant) { > >> >> + // 0 values are handled later by CheckTrivialUnsignedComparison(). > >> >> + if (Value == 0) > >> >> + return; > >> >> + > >> >> BinaryOperatorKind op = E->getOpcode(); > >> >> QualType OtherT = Other->getType(); > >> >> QualType ConstantT = Constant->getType(); > >> >> + QualType CommonT = E->getLHS()->getType(); > >> >> if (S.Context.hasSameUnqualifiedType(OtherT, ConstantT)) > >> >> return; > >> >> assert((OtherT->isIntegerType() && ConstantT->isIntegerType()) > >> >> && "comparison with non-integer type"); > >> >> // FIXME. handle cases for signedness to catch (signed char)N == > 200 > >> >> > >> >> Does this patch fix this FIXME? > >> > > >> > Yes. FIXME removed, added test case. > >> >> > >> >> > >> >> - IntRange OtherRange = IntRange::forValueOfType(S.Context, OtherT); > >> >> - IntRange LitRange = GetValueRange(S.Context, Value, > >> >> Value.getBitWidth()); > >> >> - if (OtherRange.Width >= LitRange.Width) > >> >> + > >> >> + bool ConstantSigned = ConstantT->isSignedIntegerType(); > >> >> + bool OtherSigned = OtherT->isSignedIntegerType(); > >> >> + bool CommonSigned = CommonT->isSignedIntegerType(); > >> >> > >> >> Why are you getting rid of the IntRange usage? Granted, we didn't > >> >> really have any good testcases, but it does add power to the analysis > >> >> in some cases. > >> > > >> > For my use, IntRange didn't add any value. Everything I needed, I > >> > could > >> > just get from the APSInt. The only difference was what width I used > for > >> > Other. IntRange does truncate the enum width so that different values > >> > will > >> > be considered out of range when comparing against enums. I factored > out > >> > the > >> > width into a variable. The current code will remove the existing > >> > warnings > >> > in warn-enum-compare.cpp. The code in the comments would have > preserved > >> > them. > >> > >> It does add value in cases other than enums; it can recognize > >> bitfields and knows some tricks with binary "&", logical operators in > >> C, etc. > >> > > IntRange doesn't appear to take those special cases into consideration. > > From looking at the code, it appears to special case enum, otherwise it > > falls back to ASTContext::getIntWdith(). > > Oh! I was assuming the code was using the GetExprRange() function, > but it looks like it isn't for reasons I don't really understand. > > -Eli > GetExprRange() looks promising for a tighter bound on the bit range. I will leave a FIXME to investigate it further.
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