RFR: 8332442: C2: refactor Mod cases in Compile::final_graph_reshaping_main_switch()

[Roland Westrelin]

On Thu, 5 Sep 2024 21:01:00 GMT, Kangcheng Xu <kxu at openjdk.org> wrote:

> Hello all. This patch addresses [JDK-8332442](https://bugs.openjdk.org/browse/JDK-8332442) and refactors `Op_ModI`/`Op_ModL`/`Op_UModI`/`Op_UModL` cases in `DIVMOD` transforamtions. The purpose of the transformation to convert adjacent div `/`  and mod `%` operations of the same operands into one should the platform support this feature (e.g., x86-64).
> 
> I took the liberty adding _signed_ DIVMOD nodes (i.e., `DIV_MOD_I` and `DIV_MOD_L`) to the `IRNode` class constants as they are previously missing. Please let me know if they were left intentionally and if there are any other concerns. Thanks!
> 
> ~This will be a draft PR before GHA tests are confirmed passing.~

src/hotspot/share/opto/compile.cpp line 3163:

> 3161: }
> 3162: 
> 3163: void Compile::handle_div_mod_op(Node* n, int div_op, int div_mod_op, bool is_unsigned) {

I would pass `bt` here instead of both `div_op` and `div_mod_op`.

src/hotspot/share/opto/compile.cpp line 3174:

> 3172:   }
> 3173: 
> 3174:   BasicType bt = div_op == Op_DivI || div_op == Op_UDivI ? T_INT : T_LONG;

and add a new function `Op_DivMod(BasicType bt, bool is_unsigned)` similar to `Op_ConIL` that would replace `div_mod_op` here.

test/hotspot/jtreg/compiler/c2/TestDivModNodes.java line 45:

> 43:     @Test
> 44:     @Arguments(values = {Argument.RANDOM_EACH, Argument.RANDOM_EACH})
> 45:     @IR(counts = {IRNode.DIV_MOD_I, "1" })

Running the test with both `UseDivMod` on and off and adding the corresponding IR rules would be nice.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20877#discussion_r1750105333
PR Review Comment: https://git.openjdk.org/jdk/pull/20877#discussion_r1750106629
PR Review Comment: https://git.openjdk.org/jdk/pull/20877#discussion_r1750110873