[ConstantFold] fp_binop undef, undef --> undef

These are uncontroversial and independent of a proposed LangRef edits (D44216).

I tried to fix tests that would fold away:
rL327004
rL327028
rL327030
rL327034

I'm not sure if the Reassociate tests are meaningless yet, but they probably will be 
as we add more folds, so if anyone has suggestions or wants to fix those, please do.

Differential Revision: https://reviews.llvm.org/D44258

llvm-svn: 327058
diff --git a/llvm/test/Transforms/Reassociate/fp-expr.ll b/llvm/test/Transforms/Reassociate/fp-expr.ll
index d0ad555..e616c52 100644
--- a/llvm/test/Transforms/Reassociate/fp-expr.ll
+++ b/llvm/test/Transforms/Reassociate/fp-expr.ll
@@ -1,10 +1,11 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt -S -reassociate < %s | FileCheck %s
 
 define void @test1() {
 ; CHECK-LABEL: @test1(
 ; CHECK-NEXT:    [[T1:%.*]] = tail call <4 x float> @blam()
 ; CHECK-NEXT:    [[T1_NEG:%.*]] = fsub fast <4 x float> <float -0.000000e+00, float -0.000000e+00, float -0.000000e+00, float -0.000000e+00>, [[T1]]
-; CHECK-NEXT:    [[T24:%.*]] = fadd fast <4 x float> [[T1_NEG]], fadd (<4 x float> undef, <4 x float> undef)
+; CHECK-NEXT:    [[T24:%.*]] = fadd fast <4 x float> [[T1_NEG]], undef
 ; CHECK-NEXT:    tail call void @wombat(<4 x float> [[T24]])
 ; CHECK-NEXT:    ret void
 ;
@@ -19,7 +20,7 @@
 ; CHECK-LABEL: @test2(
 ; CHECK-NEXT:    [[T15:%.*]] = fsub fast half undef, undef
 ; CHECK-NEXT:    [[T15_NEG:%.*]] = fsub fast half 0xH8000, [[T15]]
-; CHECK-NEXT:    [[T18:%.*]] = fadd fast half [[T15_NEG]], fadd (half undef, half undef)
+; CHECK-NEXT:    [[T18:%.*]] = fadd fast half [[T15_NEG]], undef
 ; CHECK-NEXT:    ret half [[T18]]
 ;
   %t15 = fsub fast half undef, undef