[SelectionDAG] Set ISD::FPOWI to Expand by default

Summary:
Currently FPOWI defaults to Legal and LegalizeDAG.cpp turns Legal into Expand for this opcode because Legal is a "lie".

This patch changes the default for this opcode to Expand and removes the hack from LegalizeDAG.cpp. It also removes all the code in the targets that set this opcode to Expand themselves since they can just rely on the default.

Reviewers: spatel, RKSimon, efriedma

Reviewed By: RKSimon

Subscribers: jfb, dschuff, sbc100, jgravelle-google, nemanjai, javed.absar, andrew.w.kaylor, llvm-commits

Differential Revision: https://reviews.llvm.org/D33530

llvm-svn: 304215
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
index 31a5ca1..8143770 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
@@ -84,8 +84,8 @@
                     ISD::SETULT, ISD::SETULE, ISD::SETUGT, ISD::SETUGE})
       setCondCodeAction(CC, T, Expand);
     // Expand floating-point library function operators.
-    for (auto Op : {ISD::FSIN, ISD::FCOS, ISD::FSINCOS, ISD::FPOWI, ISD::FPOW,
-                    ISD::FREM, ISD::FMA})
+    for (auto Op : {ISD::FSIN, ISD::FCOS, ISD::FSINCOS, ISD::FPOW, ISD::FREM,
+                    ISD::FMA})
       setOperationAction(Op, T, Expand);
     // Note supported floating-point library function operators that otherwise
     // default to expand.