[llvm] [APFloat] Correct semantics of minimum/maximum for signaling NaN arguments (PR #109976)

[Alex Bradbury via llvm-commits]

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@@ -607,13 +607,16 @@ TEST(APFloatTest, Minimum) {
   APFloat zp(0.0);
   APFloat zn(-0.0);
   APFloat nan = APFloat::getNaN(APFloat::IEEEdouble());
+  APFloat snan = APFloat::getSNaN(APFloat::IEEEdouble());
 
   EXPECT_EQ(1.0, minimum(f1, f2).convertToDouble());
   EXPECT_EQ(1.0, minimum(f2, f1).convertToDouble());
   EXPECT_EQ(-0.0, minimum(zp, zn).convertToDouble());
   EXPECT_EQ(-0.0, minimum(zn, zp).convertToDouble());
   EXPECT_TRUE(std::isnan(minimum(f1, nan).convertToDouble()));
   EXPECT_TRUE(std::isnan(minimum(nan, f1).convertToDouble()));
+  EXPECT_TRUE(maximum(snan, f1).isNaN());
+  EXPECT_FALSE(maximum(snan, f1).isSignaling());
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asb wrote:

I'm not sure to what degree I should try to closely match the current APFloat implementation vs what the IEEE spec requires. To my cursory reading it looks like it only specifies "a" quiet NaN - but perhaps there's more detail on preserving payload and signbit for NaN operands elsewhere?

https://github.com/llvm/llvm-project/pull/109976