[RISCV][GISel] Support s32/s64 G_FSUB/FDIV/FNEG without F/D extensions.

Use libcalls for G_FSUB/FDIV. Use integer operations for G_FNEG.

Copy most of the IR tests for arithmetic from SelectionDAG.

Author: topperc

llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp

@@ -491,20 +491,14 @@ RISCVLegalizerInfo::RISCVLegalizerInfo(const RISCVSubtarget &ST)
 
   // FP Operations
 
-  getActionDefinitionsBuilder({G_FSUB, G_FDIV, G_FNEG})
-      .legalFor(ST.hasStdExtF(), {s32})
-      .legalFor(ST.hasStdExtD(), {s64})
-      .legalFor(ST.hasStdExtZfh(), {s16});
-
-  // FIXME: Merge with FSUB/FDIV/etc when we use libcalls for them.
   getActionDefinitionsBuilder(
-      {G_FADD, G_FMUL, G_FMA, G_FSQRT, G_FMAXNUM, G_FMINNUM})
+      {G_FADD, G_FSUB, G_FMUL, G_FDIV, G_FMA, G_FSQRT, G_FMAXNUM, G_FMINNUM})
       .legalFor(ST.hasStdExtF(), {s32})
       .legalFor(ST.hasStdExtD(), {s64})
       .legalFor(ST.hasStdExtZfh(), {s16})
       .libcallFor({s32, s64});
 
-  getActionDefinitionsBuilder(G_FABS)
+  getActionDefinitionsBuilder({G_FNEG, G_FABS})
       .legalFor(ST.hasStdExtF(), {s32})
       .legalFor(ST.hasStdExtD(), {s64})
       .legalFor(ST.hasStdExtZfh(), {s16})