[llvm] [SDAG] Add missing float type legalizations for FMODF (PR #128055)

[Benjamin Maxwell via llvm-commits]

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@@ -2616,6 +2624,18 @@ bool SelectionDAG::expandMultipleResultFPLibCall(
 
   auto [Call, CallChain] = TLI->LowerCallTo(CLI);
 
+  if (CallRetResNo && !Node->hasAnyUseOfValue(*CallRetResNo)) {
+    // This is needed for x87, which uses a floating-point stack. If (for
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MacDue wrote:

> I was thinking X86ISD::PopX87Reg would just lower to the same COPY we currently generate for CopyFromReg; whether that actually lowers to a pop would be decided later.

This works quite well :+1: I've updated X86 call lowering to use an `X86ISD::POP_FROM_X87_REG` to handle these results -- and removed any hacks from the generic SDAG expansion. 

https://github.com/llvm/llvm-project/pull/128055