[PATCH] D41338: [CodeGen] lower math intrinsics to finite version of libcalls when possible (PR35672)

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.





================
Comment at: lib/CodeGen/SelectionDAG/LegalizeDAG.cpp:4049
   case ISD::STRICT_FEXP:
-    Results.push_back(ExpandFPLibCall(Node, RTLIB::EXP_F32, RTLIB::EXP_F64,
-                                      RTLIB::EXP_F80, RTLIB::EXP_F128,
-                                      RTLIB::EXP_PPCF128));
+    if (CanUseFiniteLibCall && DAG.getLibInfo().has(LibFunc_exp_finite))
+      Results.push_back(ExpandFPLibCall(Node, RTLIB::EXP_FINITE_F32,
----------------
hfinkel wrote:
> efriedma wrote:
> > "getLibInfo().has(LibFunc_exp_finite)" probably isn't the right check.  There are three __exp*_finite variants; each of them may or may not be legal, and you need to check that the long double variant actually accepts the input float type.
> > 
> > Also, it looks like TargetLibraryInfo doesn't contain the appropriate checks to disable them (it assumes any non-Windows platform has __exp_finite, which is clearly false).
> > and you need to check that the long double variant actually accepts the input float type.
> 
> How would we check this?
> 
> > (it assumes any non-Windows platform has __exp_finite, which is clearly false).
> 
> Hrmm. We could start with disabling them for any non-GNU triple.
For figuring out whether the long-double variant is the one we need, I guess TargetLibraryInfo should know?  We need to avoid generating a call with undefined behavior somehow.  And we probably need to eventually teach this code how to generate a call to __expf128_finite when it's available.


https://reviews.llvm.org/D41338