Commit55c4c45

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Fixed match expression is evaluated twice if it returns a struct union (dotnet#5720)

* Thanks to Don Syme, we have a fix* Added test

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Lines changed: 6 additions & 1 deletion

Original file line number	Diff line number	Diff line change
`@@ -907,6 +907,11 @@ let CompilePatternBasic`
`907`	`907`	`else`
`908`	`908`	`None,true)`
`909`	`909`
	`910`	`+andIsCopyableInputExpr origInputExpr=`
	`911`	`+match origInputExprwith`
	`912`	`+\| Expr.Op(TOp.LValueOp(LByrefGet, v),[],[],_)whennot v.IsMutable->true`
	`913`	`+\|_->false`
	`914`	`+`
`910`	`915`	`andChoosePreBinder simulSetOfEdgeDiscrims subexpr=`
`911`	`916`	`match simulSetOfEdgeDiscrimswith`
`912`	`917`	`// Very simple 'isinst' tests: put the result of 'isinst' in a local variable`
`@@ -939,7 +944,7 @@ let CompilePatternBasic`
`939`	`944`	`letargExpr= GetSubExprOfInput subexpr`
`940`	`945`	`letargExpr=`
`941`	`946`	`match argExpr,_origInputExprOptwith`
`942`		`-\| Expr.Val(v1,_,_), Some origInputExprwhen valEq origInputVal v1.Deref-> origInputExpr`
	`947`	`+\| Expr.Val(v1,_,_), Some origInputExprwhen valEq origInputVal v1.Deref&& IsCopyableInputExpr origInputExpr-> origInputExpr`
`943`	`948`	`\|_-> argExpr`
`944`	`949`	`letvOpt,addrExp,_readonly,_writeonly= mkExprAddrOfExprAux gtruefalse NeverMutates argExpr None matchm`
`945`	`950`	`match vOptwith`

Lines changed: 7 additions & 0 deletions

Original file line number	Diff line number	Diff line change
@@ -249,3 +249,10 @@ let [<Test>] ``can properly construct a struct union using FSharpValue.MakeUnion
`249`	`249`	`letc2=(fieldVals.[1]:?> int)`
`250`	`250`	`Assert.AreEqual(3456, c2)`
`251`	`251`
	`252`	+let [<Test>]``struct unions does optimization correctly on pattern matching``()=
	`253`	`+letarr= ResizeArray()`
	`254`	`+match arr.Add(1); ValueSome()with`
	`255`	`+\| ValueSome()->()`
	`256`	`+\| ValueNone->()`
	`257`	`+`
	`258`	`+ Assert.AreEqual(1, arr.Count)`

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