use afn for int_to_fp and add comments

Author: paperchalice

llvm/lib/Target/PowerPC/PPCISelLowering.cpp

@@ -8905,10 +8905,13 @@ SDValue PPCTargetLowering::LowerINT_TO_FP(SDValue Op,
     // be lost at this stage, but is below the single-precision rounding
     // position.
     //
-    // However, if -enable-unsafe-fp-math is in effect, accept double
+    // However, if afn is in effect, accept double
     // rounding to avoid the extra overhead.
+    // FIXME: Currently INT_TO_FP can't support fast math flags because
+    // of nneg flag, thus Op->getFlags().hasApproximateFuncs() is always
+    // false.
     if (Op.getValueType() == MVT::f32 && !Subtarget.hasFPCVT() &&
-        !Op->getFlags().hasNoFPExcept()) {
+        !Op->getFlags().hasApproximateFuncs()) {
 
       // Twiddle input to make sure the low 11 bits are zero.  (If this
       // is the case, we are guaranteed the value will fit into the 53 bit

llvm/test/CodeGen/PowerPC/i64_fp_round.ll

@@ -55,27 +55,4 @@ entry:
   ret float %conv
 }
 
-define float @test_constrained(i64 %x) nounwind readnone {
-; Also check that with fpexcept.ignore we do not get that extra
-; code sequence.  Simply verify that there is no "isel" present.
-; CHECK-LABEL: test_constrained:
-; CHECK:       # %bb.0: # %entry
-; CHECK-NEXT:    std 3, -8(1)
-; CHECK-NEXT:    lfd 0, -8(1)
-; CHECK-NEXT:    xscvsxddp 0, 0
-; CHECK-NEXT:    frsp 1, 0
-; CHECK-NEXT:    blr
-;
-; CHECK-NO-ISEL-LABEL: test_constrained:
-; CHECK-NO-ISEL:       # %bb.0: # %entry
-; CHECK-NO-ISEL-NEXT:    std 3, -8(1)
-; CHECK-NO-ISEL-NEXT:    lfd 0, -8(1)
-; CHECK-NO-ISEL-NEXT:    xscvsxddp 0, 0
-; CHECK-NO-ISEL-NEXT:    frsp 1, 0
-; CHECK-NO-ISEL-NEXT:    blr
-entry:
-  %conv = call float @llvm.experimental.constrained.sitofp.f32.i64(i64 %x, metadata !"round.dynamic", metadata !"fpexcept.ignore")
-  ret float %conv
-}
-
-declare float @llvm.experimental.constrained.sitofp.f32.i64(i64, metadata, metadata)
+; TODO: Add sitofp afn test.