[llvm-dev] alloca combining, not (yet) possible ?
Caldarale, Charles R via llvm-dev
llvm-dev at lists.llvm.org
Mon Aug 31 05:30:39 PDT 2015
> From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of Nat! via llvm-dev
> Subject: [llvm-dev] alloca combining, not (yet) possible ?
> I tried to get llvm (3.7) to optimize superflous allocas away, but
> so far I haven't figured out how. Should I adorn something with
> some attributes ?
> void g( void)
> struct a_b x;
> struct a_b y;
> x.a = 1;
> x.b = 2;
> f( &x);
> // x no longer needed
> // expect y to reuse x space
> y.a = 1;
> y.b = 3;
> f( &y);
You have not provided us with the declaration for f(). Unless its argument is marked with the nocapture attribute, the compilation of g() cannot assume that f() has not retained a pointer to the x struct and is using it in the second call.
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