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diff --git a/chapter15/README.md b/chapter15/README.md index 1ce5badf..e384e7ce 100644 --- a/chapter15/README.md +++ b/chapter15/README.md @@ -127,6 +127,12 @@ from a distinct New can bypass the allocation to its memory input. Mere node inequality is insufficient: a Phi or cast can still denote the allocated object. Array length is set by a subsequent Store; the array body is zeroed by New. Array accesses retain their existing control input as the bounds-check proxy. +When pushing a Load through a memory Phi, its control must dominate the +Region's immediate dominator, so both predecessor loads can retain that check. +A check at the Region or below it cannot be copied onto the predecessors. +For example, a Load guarded by `if (a# > 1)` must not move above that branch +just because its memory comes from an earlier Phi. Memory ordering alone does +not prove that `a[1]` is in bounds. Both schedulers follow an alias through MemMerge to find New's memory effect. MemMerge itself does not overwrite memory, but must not hide the ordering of |