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

[Matt Arsenault via llvm-commits]

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@@ -583,115 +583,62 @@ define { half, half } @v_fneg_add_multi_use_fneg_x_f16(half %a, half %b, half %c
 
 ; This one asserted with -enable-no-signed-zeros-fp-math
 define amdgpu_ps half @fneg_fadd_0_f16(half inreg %tmp2, half inreg %tmp6, <4 x i32> %arg) #0 {
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arsenm wrote:

Lots of codegen changes in these tests, these should get the flag added to the content 

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