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This is the fix for #12333
The fix in #6899 missed a case - We represent zero values in two ways
Simple constants like integers getExpr.Const (Const.Zero, _, _) . These are emitted near line 6374 of IlxGen.fs
"ilzero" ILASM nodes EI_ilzero. These come from Unchecked.defaultof which is what we generate for "ColorF()" default struct initializers. These go through GenDefaultValue in IlxGen and create a new temp local which we assume is zero init.
Bug #6899 was about cases where for (1) we were not zero-init'ing in code that can take backward branches (loops and let rec tailcalls). However for (2) we can also get exposed to the same problem
Note the bug only occurs for
(a)
let mutable
initialized using struct default initializers in loops(b) there are enough structs around to get to reuse the initialization temporary later on.
I'll add the test case, and let CI run through and see if exist tests catch this for codegen