[llvm] [APFloat] Fix `IEEEFloat::addOrSubtractSignificand` and `IEEEFloat::normalize` (PR #98721)

[Thorsten Schütt via llvm-commits]

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@@ -1796,35 +1797,55 @@ lostFraction IEEEFloat::addOrSubtractSignificand(const IEEEFloat &rhs,
   /* Subtraction is more subtle than one might naively expect.  */
   if (subtract) {
     IEEEFloat temp_rhs(rhs);
+    auto lost_fraction_is_from_rhs = false;
 
     if (bits == 0)
       lost_fraction = lfExactlyZero;
     else if (bits > 0) {
       lost_fraction = temp_rhs.shiftSignificandRight(bits - 1);
+      lost_fraction_is_from_rhs = true;
       shiftSignificandLeft(1);
     } else {
       lost_fraction = shiftSignificandRight(-bits - 1);
       temp_rhs.shiftSignificandLeft(1);
     }
 
     // Should we reverse the subtraction.
-    if (compareAbsoluteValue(temp_rhs) == cmpLessThan) {
-      carry = temp_rhs.subtractSignificand
-        (*this, lost_fraction != lfExactlyZero);
+    auto cmp_result = compareAbsoluteValue(temp_rhs);
+    if (cmp_result == cmpLessThan) {
+      auto borrow = false;
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tschuett wrote:

https://llvm.org/docs/CodingStandards.html#use-auto-type-deduction-to-make-code-more-readable
I would argue that the return type of `compareAbsoluteValue` is not obvious from the context.

https://github.com/llvm/llvm-project/pull/98721