[llvm] [DAGCombiner] Remove `NoSignedZerosFPMath` uses in `visitFADD` (PR #160635)

[Matt Arsenault via llvm-commits]

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@@ -737,78 +684,45 @@ define amdgpu_ps half @fneg_fadd_0_f16(half inreg %tmp2, half inreg %tmp6, <4 x
 ; function attribute unsafe-fp-math automatically. Combine with the previous test
 ; when that is done.
 define amdgpu_ps half @fneg_fadd_0_nsz_f16(half inreg %tmp2, half inreg %tmp6, <4 x i32> %arg) #2 {
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arsenm wrote:

Check the comment above, should this copy be deleted? 

https://github.com/llvm/llvm-project/pull/160635