[llvm] add `frexp`/`ldexp` expansion in `ExpandIrInsts` (PR #208556)

[Matt Arsenault via llvm-commits]

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@@ -1276,7 +1492,22 @@ static bool runImpl(Function &F, const TargetLowering &TLI,
       MaxLegalDivRemBitWidth >= IntegerType::MAX_INT_BITS;
   bool DisableFrem = !FRemExpander::shouldExpandAnyFremType(TLI);
 
-  if (DisableExpandLargeFp && DisableFrem && DisableExpandLargeDivRem)
+  static constexpr std::array ExpandableTypes{MVT::f32, MVT::f64, MVT::f128};
+  auto NeedsExpand = [&](EVT VT, unsigned ISDOp, RTLIB::Libcall LC) {
+    // For f16/bf16 LC is UNKNOWN_LIBCALL, they are handled via promotion.
+    return LC != RTLIB::UNKNOWN_LIBCALL &&
+           TLI.getOperationAction(ISDOp, VT) == TargetLowering::Expand &&
+           Libcalls.getLibcallImpl(LC) == RTLIB::Unsupported;
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arsenm wrote:

Can you make this a proper helper function? Ideally we would first migrate all the targets onto using the LibCall action for these operations. Then the logic would be `Expand || (Libcall && getLibcallImpl() == Unsupported`

https://github.com/llvm/llvm-project/pull/208556