[clang] [flang] [llvm] Fix/172049 loop vectorize sigfpe (PR #172094)

[Luke Lau via llvm-commits]

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@@ -2907,6 +2907,10 @@ uint64_t LoopVectorizationCostModel::getPredBlockCostDivisor(
   uint64_t BBFreq = getBFI().getBlockFreq(BB).getFrequency();
   assert(HeaderFreq >= BBFreq &&
          "Header has smaller block freq than dominated BB?");
+  // Guard against division by zero when BBFreq is 0.
+  // In such cases, return 1 to avoid undefined behavior.
+  if (BBFreq == 0)
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lukel97 wrote:

FP division by zero isn't undefined behaviour, it should return -Inf. But in any case BlockFrequencyInfo should never return a zero frequency. If you add an assert here you'll see that BBFreq is never zero

https://github.com/llvm/llvm-project/pull/172094