Closed
Description
I noticed the following diff with physical promotion enabled:
+22 (+733.33%) : 48321.dasm - Microsoft.CodeAnalysis.CSharp.Syntax.NullableContextStateMap:GetContextForFileStart():Microsoft.CodeAnalysis.CSharp.Syntax.NullableContextState
@@ -8,20 +8,29 @@
; Final local variable assignments
;
;# V00 OutArgs [V00 ] ( 1, 1 ) struct ( 0) [rsp+00H] do-not-enreg[XS] addr-exposed "OutgoingArgSpace"
-;* V01 tmp1 [V01 ] ( 0, 0 ) struct ( 8) zero-ref do-not-enreg[SF] ld-addr-op "NewObj constructor temp"
+; V01 tmp1 [V01,T00] ( 4, 8 ) struct ( 8) [rsp+00H] do-not-enreg[SF] ld-addr-op "NewObj constructor temp"
+;* V02 tmp2 [V02 ] ( 0, 0 ) int -> zero-ref "V01.[000..004)"
+;* V03 tmp3 [V03,T01] ( 0, 0 ) ubyte -> zero-ref "V01.[004..005)"
+;* V04 tmp4 [V04,T02] ( 0, 0 ) ubyte -> zero-ref "V01.[005..006)"
;
-; Lcl frame size = 0
+; Lcl frame size = 8
G_M10451_IG01: ; bbWeight=1, gcrefRegs=0000 {}, byrefRegs=0000 {}, byref, nogc <-- Prolog IG
- ;; size=0 bbWeight=1 PerfScore 0.00
+ push rax
+ ;; size=1 bbWeight=1 PerfScore 1.00
G_M10451_IG02: ; bbWeight=1, gcrefRegs=0000 {}, byrefRegs=0000 {}, byref
xor eax, eax
- ;; size=2 bbWeight=1 PerfScore 0.25
+ mov dword ptr [rsp], eax
+ mov byte ptr [rsp+04H], 0
+ mov byte ptr [rsp+05H], 0
+ mov rax, qword ptr [rsp]
+ ;; size=19 bbWeight=1 PerfScore 4.25
G_M10451_IG03: ; bbWeight=1, epilog, nogc, extend
+ add rsp, 8
ret
- ;; size=1 bbWeight=1 PerfScore 1.00
+ ;; size=5 bbWeight=1 PerfScore 1.25
-; Total bytes of code 3, prolog size 0, PerfScore 1.55, instruction count 2, allocated bytes for code 3 (MethodHash=08d0d72c) for method Microsoft.CodeAnalysis.CSharp.Syntax.NullableContextStateMap:GetContextForFileStart():Microsoft.CodeAnalysis.CSharp.Syntax.NullableContextState
+; Total bytes of code 25, prolog size 1, PerfScore 9.00, instruction count 8, allocated bytes for code 25 (MethodHash=08d0d72c) for method Microsoft.CodeAnalysis.CSharp.Syntax.NullableContextStateMap:GetContextForFileStart():Microsoft.CodeAnalysis.CSharp.Syntax.NullableContextState
; ============================================================This is the result of a zero init of the struct + read back + return, with the struct having two padding bytes at the end. We would need to teach the store forwarding optimization in lowering about padding to catch this (or alternatively allow RETURN(FIELD_LIST)).
Normal promotion just sees a block init with holes and DNERs it.