[llvm] AMDGPU/GlobalISel: Partially move constant selection to patterns (PR #100786)

[Joe Nash via llvm-commits]

================
@@ -2163,6 +2163,11 @@ def : GCNPat <
   (S_MOV_B32 $ga)
 >;
 
+def : GCNPat <
----------------
Sisyph wrote:

```suggestion
foreach pred = [NotHasTrue16BitInsts, UseFakeTrue16Insts] in {                                                                                                                                                                   
  let True16Predicate = pred in                                                                                                                                                                                                  
  def : GCNPat <                                                                                                                                                                                                                 
    (VGPRImm<(i16 imm)>:$imm),                                                                                                                                                                                                   
    (V_MOV_B32_e32 imm:$imm)                                                                                                                                                                                                     
  >;                                                                                                                                                                                                                             
}                                                                                                                                                                                                                                
let True16Predicate = UseRealTrue16Insts in                                                                                                                                                                                      
def : GCNPat <                                                                                                                                                                                                                   
  (VGPRImm<(i16 imm)>:$imm),                                                                                                                                                                                                     
  (V_MOV_B16_t16_e64 0, imm:$imm, 0)                                                                                                                                                                                             
>;
```

https://github.com/llvm/llvm-project/pull/100786