[compiler-rt] [compiler-rt][nsan] Add support for nan detection (PR #101531)

[Alexander Shaposhnikov via llvm-commits]

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@@ -444,6 +444,25 @@ int32_t checkFT(const FT value, ShadowFT Shadow, CheckTypeT CheckType,
   const InternalFT check_value = value;
   const InternalFT check_shadow = Shadow;
 
+  // We only check for NaNs in the value, not the shadow.
+  if (flags().check_nan && isnan(check_value)) {
+    GET_CALLER_PC_BP;
+    BufferedStackTrace stack;
+    stack.Unwind(pc, bp, nullptr, false);
+    if (GetSuppressionForStack(&stack, CheckKind::Consistency)) {
+      // FIXME: optionally print.
+      return flags().resume_after_suppression ? kResumeFromValue
+                                              : kContinueWithShadow;
+    }
+    Decorator D;
+    Printf("%s", D.Warning());
+    Printf("WARNING: NumericalStabilitySanitizer: NaN detected\n");
+    Printf("%s", D.Default());
+    stack.Print();
+    // Performing other tests for NaN values is meaningless when dealing with numbers.
+    return kResumeFromValue;
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alexander-shaposhnikov wrote:

this doesn't respect the option `halt_on_error`, see
```
 if (flags().halt_on_error) {
    if (common_flags()->abort_on_error)
      Printf("ABORTING\n");
    else
      Printf("Exiting\n");
    Die();
  }
```
below (lines 575 - 595).
We need the same here + need to test it.

https://github.com/llvm/llvm-project/pull/101531