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JIT: avoid fp divide by zero in profile synthesis #113396

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Mar 12, 2025
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JIT: avoid fp divide by zero in profile synthesis #113396

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11 changes: 9 additions & 2 deletions src/coreclr/jit/fgprofilesynthesis.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1411,12 +1411,19 @@ void ProfileSynthesis::GaussSeidelSolver()
countVector[block->bbNum] = newWeight;

// Remember max absolute and relative change
// (note rel residual will be infinite at times, that's ok)
// (note rel residual will be as large as 1e9 at times, that's ok)
//
// Note we are using a "point" bound here ("infinity norm") rather than say
// computing the L2-norm of the entire residual vector.
//
weight_t const blockRelResidual = change / oldWeight;
weight_t const smallFractionOfChange = 1e-9 * change;
weight_t relDivisor = oldWeight;
if (relDivisor < smallFractionOfChange)
{
relDivisor = smallFractionOfChange;
}

weight_t const blockRelResidual = change / relDivisor;
Comment on lines +1419 to +1426
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Wondering can't it just be something like weight_t const blockRelResidual = change / (oldWeight + 1e-10)?

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Yeah, that would have worked too.

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@AndyAyersMS AndyAyersMS Apr 23, 2025 •
edited
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Turns out @hez2010 had a better fix. If change is zero we will end up with 0.0 / 0.0 which causes an "invalid FP operation" exception.


if ((relResidualBlock == nullptr) || (blockRelResidual > relResidual))
{
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