[Bug rtl-optimization/56598] New: Optimizer can't invert conditional when inlining a bool function

[msharov at users dot sourceforge.net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56598



             Bug #: 56598

           Summary: Optimizer can't invert conditional when inlining a

                    bool function

    Classification: Unclassified

           Product: gcc

           Version: 4.7.2

            Status: UNCONFIRMED

          Severity: minor

          Priority: P3

         Component: rtl-optimization

        AssignedTo: unassig...@gcc.gnu.org

        ReportedBy: msha...@users.sourceforge.net





Created attachment 29640

  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29640

Simple test case and its asm



When a bool macro like #define X(i) (i==3) is replaced with a static inline

bool function, the optimizer sometimes generates tangled control flow. With

code blocks ABCD the jumps go A->C->B->D. If the macro is used, the compiler

can invert the conditional and emit ACBD with two fewer jmps. In the attached

test case, func1 has .L3-.L4 block that is jumped into, out of, and over.

Swapping the .L2-.L3 and .L3-.L4 blocks would produce the simpler control flow

in func2. The test case is compiled with -Os, on x86_64. -O2 and -O3 also

produce the same behavior, but require a larger test case to avoid path

unrolling. C++ compiler must be used. The same test case compiled as C produces

identical func1 and func2.