id decorated twice with the same decoration

[maarquitos14]

target datalayout = "e-p:32:32-i64:64-v16:16-v24:32-v32:32-v48:64-v96:128-v192:256-v256:256-v512:512-v1024:1024"
target triple = "spir-unknown-unknown"

define void @foo(float %1, float %2) {
entry:
  %oltRes = fcmp nnan olt float %1,  %2, !spirv.Decorations !1
  ret void
}

!1 = !{!2}
!2 = !{i32 40, i32 0} ; 40 is FPFastMathMode

The code above results in the following SPIR-V Module:

119734787 67072 393230 11 0
2 Capability Addresses
2 Capability Linkage
2 Capability Kernel
5 ExtInstImport 1 "OpenCL.std"
3 MemoryModel 1 2
3 Source 0 0
3 Name 5 "foo"
4 Name 8 "entry"
4 Name 10 "oltRes"
5 Decorate 5 LinkageAttributes "foo" Export
4 Decorate 10 FPFastMathMode 1
4 Decorate 10 FPFastMathMode 0
2 TypeVoid 2
3 TypeFloat 3 32
5 TypeFunction 4 2 3 3
2 TypeBool 9


5 Function 2 5 0 4
3 FunctionParameter 3 6
3 FunctionParameter 3 7

2 Label 8
5 FOrdLessThan 9 10 6 7
1 Return

1 FunctionEnd

The module contains FPFastMathMode decoration twice for id 10. According to the spec

It is invalid to decorate any given or structure member more than one time with the same decoration, unless explicitly allowed below for a specific decoration.

FPFastMathMode does not explicitly allow it, so this is illegal.

[maarquitos14]

In the SPIRV BE it was decided to ignore !spirv.Decorations for fp flags. The reason behind this decision was that metadata like !spirv.Decorations was meant to map SPIR-V entities that don't have obvious counterparts in LLVM IR. However, FP flags do have an obvious match. Link to the discussion: llvm/llvm-project#146941 (comment)

Should we match SPIRV BE's behavior in the translator?