[llvm] Enable logf128 constant folding for hosts with 128bit long double (PR #104929)

[David Green via llvm-commits]

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@@ -1781,11 +1782,19 @@ Constant *ConstantFoldFP(double (*NativeFP)(double), const APFloat &V,
   return GetConstantFoldFPValue(Result, Ty);
 }
 
-#if defined(HAS_IEE754_FLOAT128) && defined(HAS_LOGF128)
+#if defined(HAS_IEE754_FLOAT128)
 Constant *ConstantFoldFP128(float128 (*NativeFP)(float128), const APFloat &V,
                             Type *Ty) {
   llvm_fenv_clearexcept();
-  float128 Result = NativeFP(V.convertToQuad());
+
+  if (!V.isValidIEEEQuad())
+    return nullptr;
+
+  APInt Api = V.bitcastToAPInt();
+  __uint128_t Int128 = ((__uint128_t)Api.extractBitsAsZExtValue(64, 64) << 64) +
+                       Api.extractBitsAsZExtValue(64, 0);
+  float128 Result = NativeFP(llvm::bit_cast<float128>(Int128));
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davemgreen wrote:

It might be worth having a method to abstract the two converts in this file.

https://github.com/llvm/llvm-project/pull/104929