[release/9.0-staging] JIT: revised fix for fp division issue in profile synthesis #115026
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The previous fix #113396 could still leave us trying to evaluate 0.0/0.0, which causes an invalid FP operation exception. Make sure the divisor is non-zero.
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Backport of #115005 to release/9.0-staging
/cc @AndyAyersMS
Customer Impact
Unexpected floating-point divide by zero exception. While we generally don't support running managed code with FP exceptions enabled, we also should not be generating such exceptions needlessly.
There is precedent for us back porting this kind of change, see eg: #76334
This is a revised version of a previous fix #113418. The original fix removed the divide by zero case, but allowed for 0.0/0.0, which also causes an FP exception (invalid operation).
Regression
.NET 9 added a fair amount of FP processing to the JIT that wasn't there in .NET 8.
Testing
Verified the JIT will no longer cause any FP exception from this computation.
Risk
Low, no diffs in SPMI.
Package authoring no longer needed in .NET 9
IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.
Keep in mind that we still need package authoring in .NET 8 and older versions.