[llvm] [AMDGPU] Only src0 and mandatory literals can use literal64 (PR #196456)

[Jay Foad via llvm-commits]

jayfoad wrote:

> The still remaining problem:
> 
> ```
> llvm-mc -arch=amdgcn -mcpu=gfx1250 -show-encoding <<< 'v_add_f64 v[0:1], v[0:1], lit(1)'
> 	v_add_f64_e64 v[0:1], v[0:1], lit(0x1)  ; encoding: [0x00,0x00,0x02,0xd5,0x00,0xfd,0x01,0x02,0x01,0x00,0x00,0x00,0x00,0x00,0x00,0x00]
> ```
> 
> @kosarev could you please take a look? That shall use lit32 I believe, no reason to force lit64, it was not requested. And then it is simply illegal. I.e., literal can be represented as 32-bit. If it is not then we shall issue an error here.

It looks like `lit(0x1)` here means the f64 bit pattern 0x0000000000000001, which can't be represented as lit32 because that only lets you specify the high 32 bits of an f64 value.

https://github.com/llvm/llvm-project/pull/196456