[MPS] Fix nllnd_loss_backward crash with different dtypes

[malfet]

Stack from ghstack (oldest at bottom):

• [WIP] Enable MPS inductor testing #143966
• -> [MPS] Fix nllnd_loss_backward crash with different dtypes #144170
• [MPSInductor] Add masked implementation #144084
• [MPSInductor] Add floor_div and index_expr implementation #144083
• [MPSInductor] Add remainder op #144162
• [MPSInductor] Extend constant to bool type #144167

Otherwise, invoking with torch.half inputs, but float weights will result in

(mpsFileLoc): /AppleInternal/Library/BuildRoots/b11baf73-9ee0-11ef-b7b4-7aebe1f78c73/Library/Caches/com.apple.xbs/Sources/MetalPerformanceShadersGraph/mpsgraph/MetalPerformanceShadersGraph/Core/Files/MPSGraphUtilities.mm:233:0: error: 'mps.divide' op requires the same element type for all operands and results
(mpsFileLoc): /AppleInternal/Library/BuildRoots/b11baf73-9ee0-11ef-b7b4-7aebe1f78c73/Library/Caches/com.apple.xbs/Sources/MetalPerformanceShadersGraph/mpsgraph/MetalPerformanceShadersGraph/Core/Files/MPSGraphUtilities.mm:233:0: note: see current operation: %16 = "mps.divide"(%15, %arg2) : (tensor<5x5xf16>, tensor<1xf32>) -> tensor<*xf32>
(mpsFileLoc): /AppleInternal/Library/BuildRoots/b11baf73-9ee0-11ef-b7b4-7aebe1f78c73/Library/Caches/com.apple.xbs/Sources/MetalPerformanceShadersGraph/mpsgraph/MetalPerformanceShadersGraph/Core/Files/MPSGraphUtilities.mm:233:0: error: 'mps.divide' op requires the same element type for all operands and results
(mpsFileLoc): /AppleInternal/Library/BuildRoots/b11baf73-9ee0-11ef-b7b4-7aebe1f78c73/Library/Caches/com.apple.xbs/Sources/MetalPerformanceShadersGraph/mpsgraph/MetalPerformanceShadersGraph/Core/Files/MPSGraphUtilities.mm:233:0: note: see current operation: %16 = "mps.divide"(%15, %arg2) : (tensor<5x5xf16>, tensor<1xf32>) -> tensor<*xf32>
2025-01-03 14:13:18.747151-0800 python[87772:4027380] /AppleInternal/Library/BuildRoots/b11baf73-9ee0-11ef-b7b4-7aebe1f78c73/Library/Caches/com.apple.xbs/Sources/MetalPerformanceShadersGraph/mpsgraph/MetalPerformanceShadersGraph/Core/Files/MPSGraphExecutable.mm, line 975: error 'original module failed verification'
/AppleInternal/Library/BuildRoots/b11baf73-9ee0-11ef-b7b4-7aebe1f78c73/Library/Caches/com.apple.xbs/Sources/MetalPerformanceShadersGraph/mpsgraph/MetalPerformanceShadersGraph/Core/Files/MPSGraphExecutable.mm:975: failed assertion `original module failed verification'

Test plan: python -mpytest test/inductor/test_torchinductor.py -k test_nll_loss_backward_mps should not crash

[pytorch-bot]

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[kit1980]

If divident is an integer, and divisor is some float (like "10 / 2.5"), can the type cast change results? Or this can never happen?

[malfet]

@pytorchbot merge -f "MPS tests are green"

[malfet]

If divident is an integer, and divisor is some float (like "10 / 2.5"), can the type cast change results? Or this can never happen?

It can change results from crash to some numerical value, which is imo a good thing. But in general, we are not very good about understanding, what permutations of dtypes are acceptable, and which aren't

[pytorchmergebot]

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