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772debb03a
At the moment, the LLVM IR we generate for this fn is
define internal fastcc void @AstGen.numberLiteral ... {
Entry:
...
%16 = alloca %"fmt.parse_float.decimal.Decimal(f128)", align 8
...
That `Decimal` is huuuge! It stores
pub const max_digits = 11564;
digits: [max_digits]u8,
on the stack.
It comes from `convertSlow` function, which LLVM happily inlined,
despite it being the cold path. Forbid inlining that to not penalize
callers with excessive stack usage.
Backstory: I was looking for needles memcpys in TigerBeetle, and came up
with this copyhound.zig tool for doing just that:
ee67e2ab95/src/copyhound.zig
Got curious, run it on the Zig's own code base, and looked at some of
the worst offenders.
List of worst offenders:
warning: crypto.kyber_d00.Kyber.SecretKey.decaps: 7776 bytes memcpy
warning: crypto.ff.Modulus.powPublic: 8160 bytes memcpy
warning: AstGen.numberLiteral: 11584 bytes memcpy
warning: crypto.tls.Client.init__anon_133566: 13984 bytes memcpy
warning: http.Client.connectUnproxied: 16896 bytes memcpy
warning: crypto.tls.Client.init__anon_133566: 16904 bytes memcpy
warning: objcopy.ElfFileHelper.tryCompressSection: 32768 bytes memcpy
Note from Andrew: I removed `noinline` from this commit since it should
be enough to set it to be cold.