Avoid shifting null constants in compression sequences - #17941
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This ensures that code generators will not generate an unnecessary shift instruction, even if they make no effort to detect compression sequences for null constants. It's still always possible to traverse through the sequence to find the original (null) reference. Additionally, propagate the null/non-null flags from the reference node to all of the integer-typed nodes in the sequence rather than only the truncation (l2i), and also flag the long value immediately prior to truncation as having zero in its high half. These properties hold, so the flags might as well be set.
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Jenkins test sanity all jdk11,jdk17 |
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This ensures that code generators will not generate an unnecessary shift instruction, even if they make no effort to detect compression sequences for null constants.
It's still always possible to traverse through the sequence to find the original (null) reference.
Additionally, propagate the null/non-null flags from the reference node to all of the integer-typed nodes in the sequence rather than only the truncation (
l2i), and also flag the long value immediately prior to truncation as having zero in its high half. These properties hold, so the flags might as well be set.