On Tue, 28 Apr 2026 06:11:03 GMT, Emanuel Peter <[email protected]> wrote:
>> Jatin Bhateja has updated the pull request incrementally with one additional
>> commit since the last revision:
>>
>> Remving duplicate IRNode definitions after latest mainline merge
>
> src/hotspot/share/opto/vectornode.cpp line 300:
>
>> 298: // Return the scalar opcode for the specified vector opcode and basic
>> type.
>> 299: // Returns 0 if not handled.
>> 300: int VectorNode::scalar_opcode(int vopc, BasicType bt) {
>
> Is this not the inverse of some other `VectorNode` function? Could we have
> some kind of assert/verification to check for consistency?
Hi @eme64 , consistency checks are part of VectorNode::make_scalar from where
scalar_opcod is called.
> src/hotspot/share/opto/vectornode.cpp line 1385:
>
>> 1383: sop = phase->transform(new LShiftINode(sop, con_shift));
>> 1384: sop = phase->transform(new RShiftINode(sop, con_shift));
>> 1385: }
>
> I think we have the default the wrong way around here.
> We should assume that by default we always have to do truncation, and should
> only avoid truncation if we are sure it is safe.
>
> Otherwise we might be setting ourselves up for future bugs here, and it will
> be difficult to catch them, until some fuzzer finds it.
>
> @iwanowww do you agree?
>
> See also `superword.cpp` -> `can_subword_truncate`
I had originally banked on the truncation semantics of broadcast instruction
(replicate node), but to be consistent with the Ideal graph generated if we
hand tune this transformation in java code, introduced the truncation IR.
public static void micro1(byte [] dst, byte [] src1, byte [] src2, int idx) {
ByteVector.broadcast(BSP, n1)
.lanewise(VectorOperators.ADD, ByteVector.broadcast(BSP, n2))
.intoArray(dst, idx);
}
public static void micro2(byte [] dst, byte [] src1, byte [] src2, int idx) {
ByteVector.broadcast(BSP, n1 + n2)
.intoArray(dst, idx);
}
Following is the Ideal graph generated for micro2
37 AddI === _ 31 36 [[ 88 ]] !jvms: test_subword::micro2 @ bci:9 (line 19)
87 ConI === 0 [[ 88 89 ]] #int:24
88 LShiftI === _ 37 87 [[ 89 ]] !jvms:
ByteVector$ByteSpecies::longToElementBits @ bci:2 (line 4328)
ByteVector$ByteSpecies::broadcast @ bci:3 (line 4320) ByteVector::broadcast @
bci:7 (line 673) test_subword::micro2 @ bci:11 (line 19)
89 RShiftI === _ 88 87 [[ 101 90 506 ]] !jvms:
ByteVector$ByteSpecies::longToElementBits @ bci:2 (line 4328)
ByteVector$ByteSpecies::broadcast @ bci:3 (line 4320) ByteVector::broadcast @
bci:7 (line 673) test_subword::micro2 @ bci:11 (line 19)
506 Replicate === _ 89 [[ 348 533 362 ]] #vectorz<B,64> !jvms:
ByteVector$ByteSpecies::broadcastBits @ bci:20 (line 4305)
ByteVector$ByteSpecies::broadcast @ bci:6 (line 4320) ByteVector::broadcast @
bci:7 (line 673) test_subword::micro2 @ bci:11 (line 19)
Lets wait to hear back form @iwanowww
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/25617#discussion_r3153035681
PR Review Comment: https://git.openjdk.org/jdk/pull/25617#discussion_r3153036416
