[GPU] Long compilation time/excessive ops generated

[IanWood1]

Some multi-reduction dispatches take a long time to compile. For context, https://github.com/iree-org/iree/issues/18479 identifies numerical issues with the current pipeline and https://github.com/iree-org/iree/pull/18519 should solve this issue. But the compilation time for the 'good dispatch' linked on #18479 is quite long (for me about 40 seconds). IR dumps show that a bunch of ops being generated during LLVMGPUVectorDistribute.

To Reproduce:

1. Checkout IREE at 2047f61(from Bangtian's PR)
2. Download the mlir file https://gist.github.com/IanWood1/add7f516d88b81ce8b3d819bf39c2025
3. Run iree-compile good-source2.mlir -o /dev/null --iree-hal-target-backends=rocm --iree-dispatch-creation-enable-aggressive-fusion

Additionally, following the same steps above but using main (tested at 914858fb89c028a94564b590626aab519d611e54) also exhibits long (~20 seconds) compilation times. This appears to be an unrelated (and there is a reasonable amount of ops but some very big vector.shuffle masks) since they are going down different pipelines. This should be resolved after switching pipelines.