[Issue 11506] pure evaluation should be shortcircuited

[d-bugmail at puremagic.com]

https://d.puremagic.com/issues/show_bug.cgi?id=11506


Walter Bright <bugzilla at digitalmars.com> changed:

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--- Comment #4 from Walter Bright <bugzilla at digitalmars.com> 2013-11-13 12:22:31 PST ---
Yes, bearophile's right, I forgot about nothrow.

But the compiler is a bit conservative by requiring nothrow. For throwing pure
functions, the foo()+foo() case can still be replaced with 2*foo() if the
arguments to foo are identical, even if foo throws. The obvious case of this is
the no-argument case, which bearophile mentioned.

Also, if foo() returns memory that it new'd, it cannot be elided:

    pure nothrow string foo();
    return foo() ~ foo();

so things are a bit complicated, but there's still optimization opportunity.

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