[OpenJDK 2D-Dev] New warnings in layout code

[Omair Majid]

Hi,

With a recent change to layout code in OpenJDK [1], I have started to get new
build warnings in layout code when building with gcc (5.3.1) on linux:

> /home/omajid/devel/jdk8u-jdk8u/jdk/src/share/native/sun/font/layout/IndicRearrangementProcessor.cpp: In member function ‘void IndicRearrangementP      rocessor::doRearrangementAction(LEGlyphStorage&, IndicRearrangementVerb, LEErrorCode&) const’:
> /home/omajid/devel/jdk8u-jdk8u/jdk/src/share/native/sun/font/layout/IndicRearrangementProcessor.cpp:119:30: warning: assuming signed overflow does not occur when assuming that (X + c) < X is always false [-Wstrict-overflow]
>          if (firstGlyph + 1 < firstGlyph) {
>                               ^
> /home/omajid/devel/jdk8u-jdk8u/jdk/src/share/native/sun/font/layout/IndicRearrangementProcessor.cpp:140:29: warning: assuming signed overflow does not occur when assuming that (X - c) > X is always false [-Wstrict-overflow]
>          if (lastGlyph - 1 > lastGlyph) {
>                              ^
> /home/omajid/devel/jdk8u-jdk8u/jdk/src/share/native/sun/font/layout/IndicRearrangementProcessor.cpp:172:31: warning: assuming signed overflow does not occur when assuming that (X + c) < X is always false [-Wstrict-overflow]
>          if ((firstGlyph + 2 < firstGlyph) ||
>                                ^
> /home/omajid/devel/jdk8u-jdk8u/jdk/src/share/native/sun/font/layout/IndicRearrangementProcessor.cpp:198:31: warning: assuming signed overflow does not occur when assuming that (X + c) < X is always false [-Wstrict-overflow]
>          if ((firstGlyph + 2 < firstGlyph) ||
>                                ^
> /home/omajid/devel/jdk8u-jdk8u/jdk/src/share/native/sun/font/layout/IndicRearrangementProcessor.cpp:224:30: warning: assuming signed overflow does not occur when assuming that (X - c) > X is always false [-Wstrict-overflow]
>          if ((lastGlyph - 2 > lastGlyph) ||
>                               ^
> /home/omajid/devel/jdk8u-jdk8u/jdk/src/share/native/sun/font/layout/IndicRearrangementProcessor.cpp:250:30: warning: assuming signed overflow does not occur when assuming that (X - c) > X is always false [-Wstrict-overflow]
>          if ((lastGlyph - 2 > lastGlyph) ||
>                               ^
> /home/omajid/devel/jdk8u-jdk8u/jdk/src/share/native/sun/font/layout/IndicRearrangementProcessor.cpp:276:30: warning: assuming signed overflow does not occur when assuming that (X - c) > X is always false [-Wstrict-overflow]
>          if ((lastGlyph - 2 > lastGlyph) ||

These warnings seem to be checking for overflow of signed integers, which is
undefined. These warnings were added when the variable was unsigned [2], in
which case the overflow as defined. But with the recent change [1] the variable
was made signed and this operation is no longer defined.

Are these warnings worth worrying about? Can the error condition that the
checks are supposed to be preventing still happen? Should -fno-strict-overflow
be added to the build flags of libfontmanager?

Thanks,
Omair

[1] http://hg.openjdk.java.net/jdk8u/jdk8u/jdk/rev/f556d4c82ef1
[2] http://hg.openjdk.java.net/jdk8u/jdk8u/jdk/rev/dbb4e2bdfa9e

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