8319690: [AArch64] C2 compilation hits offset_ok_for_immed: assert "c2 compiler bug"

[fg1417]

On LP64 systems, if the heap can be moved into low virtual address space (below 4GB) and the heap size is smaller than the interesting threshold of 4 GB, we can use unscaled decoding pattern for narrow klass decoding. It means that a generic field reference can be decoded by:

cast<64> (32-bit compressed reference) + field_offset

When the field_offset is an immediate, on aarch64 platform, the unscaled decoding pattern can match perfectly with a direct addressing mode, i.e., base_plus_offset, supported by LDR/STR instructions. But for certain data width, not all immediates can be encoded in the instruction field of LDR/STR [1]. The ranges are different as data widths vary.

For example, when we try to load a value of long type at offset of 1030, the address expression is (AddP (DecodeN base) 1030). Before the patch, the expression was matching with operand indOffIN(). But, for 64-bit LDR/STR, signed immediate byte offset must be in the range -256 to 255 or positive immediate byte offset must be a multiple of 8 in the range 0 to 32760 [2]. 1030 can't be encoded in the instruction field. So, after matching, when we do checking for instruction encoding, the assertion would fail.

In this patch, we're going to filter out invalid immediates when deciding if current addressing mode can be matched as base_plus_offset. We introduce indOffIN4/indOffLN4 and indOffIN8/indOffLN8 for 32-bit data type and 64-bit data type separately in the patch. E.g., for memory4, we remove the generic indOffIN/indOffLN, which matches wrong unscaled immediate range, and replace them with indOffIN4/indOffLN4 instead.

Since 8-bit and 16-bit LDR/STR instructions also support the unscaled decoding pattern, we add the addressing mode in the lists of memory1 and memory2 by introducing indOffIN1/indOffLN1 and indOffIN2/indOffLN2.

We also remove unused operands indOffI/indOffl/indOffIN/indOffLN to avoid misuse.

Tier 1-3 passed on aarch64.

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• JDK-8319690: [AArch64] C2 compilation hits offset_ok_for_immed: assert "c2 compiler bug" (Bug - P4) ⚠️ Issue is already resolved. Consider making this a "backport pull request" by setting the PR title to Backport <hash> with the hash of the original commit. See Backports.

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