c# - Is return variable automatically created by compiler? -
when going on project source code, stumbled upon method , wondered 1 thing. following 2 methods same performance/memory/compiler point of view?
public static string foo(string inputvar) { string bar = dosomething(inputvar); return bar; } public static string foo(string inputvar) { return dosomething(inputvar); } is return variable automatically created compiler?
using il disassembler (included in .net sdk/vs) can @ il generated compiler. code generated using vs2013 (not roslyn).
the top 1 gives following il:
.method public hidebysig static string foo(string inputvar) cil managed { // code size 14 (0xe) .maxstack 1 .locals init ([0] string bar, [1] string cs$1$0000) il_0000: nop il_0001: ldarg.0 il_0002: call string testil.program::dosomething(string) il_0007: stloc.0 il_0008: ldloc.0 il_0009: stloc.1 il_000a: br.s il_000c il_000c: ldloc.1 il_000d: ret } // end of method program::foo the second one:
.method public hidebysig static string foo(string inputvar) cil managed { // code size 12 (0xc) .maxstack 1 .locals init ([0] string cs$1$0000) il_0000: nop il_0001: ldarg.0 il_0002: call string testil.program::dosomething(string) il_0007: stloc.0 il_0008: br.s il_000a il_000a: ldloc.0 il_000b: ret } // end of method program::foo the difference seems first 1 creates entry in methods locals table. if optimized away jit compiler don't know.
to answer question: no, doesn't seems compiler automatically generates local variable in case, in more advanced case might (like return x * (y + z)).
edit: if turn on "optimize code" more clear:
.method public hidebysig static string foo(string inputvar) cil managed { // code size 9 (0x9) .maxstack 1 .locals init ([0] string bar) il_0000: ldarg.0 il_0001: call string testil.program::dosomething(string) il_0006: stloc.0 il_0007: ldloc.0 il_0008: ret } // end of method program::foo .method public hidebysig static string foo(string inputvar) cil managed { // code size 7 (0x7) .maxstack 8 il_0000: ldarg.0 il_0001: call string testil.program::dosomething(string) il_0006: ret } // end of method program::foo
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