[AMDGPU] Add GFX12 S_ALLOC_VGPR instruction

This patch only adds the instruction for disassembly support.

We neither have an instrinsic nor codegen support, and it is
unclear whether we actually want to ever have an intrinsic,
given the fragile semantics.

For now, it will be generated only by the backend in very specific
circumstances.

Author: jasilvanus

llvm/lib/Target/AMDGPU/SOPInstructions.td

@@ -423,6 +423,12 @@ let SubtargetPredicate = isGFX11Plus in {
   }
 } // End SubtargetPredicate = isGFX11Plus
 
+let SubtargetPredicate = isGFX12Plus in {
+  let hasSideEffects = 1, Defs = [SCC] in {
+    def S_ALLOC_VGPR : SOP1_0_32 <"s_alloc_vgpr">;
+  }
+} // End SubtargetPredicate = isGFX12Plus
+
 class SOP1_F32_Inst<string opName, SDPatternOperator Op, ValueType vt0=f32,
                     ValueType vt1=vt0> :
   SOP1_32<opName, [(set vt0:$sdst, (UniformUnaryFrag<Op> vt1:$src0))]>;
@@ -2048,6 +2054,7 @@ defm S_GET_BARRIER_STATE_M0       : SOP1_M0_Real_gfx12<0x050>;
 defm S_BARRIER_SIGNAL_IMM         : SOP1_IMM_Real_gfx12<0x04e>;
 defm S_BARRIER_SIGNAL_ISFIRST_IMM : SOP1_IMM_Real_gfx12<0x04f>;
 defm S_GET_BARRIER_STATE_IMM      : SOP1_IMM_Real_gfx12<0x050>;
+defm S_ALLOC_VGPR                 : SOP1_Real_gfx12<0x053>;
 defm S_SLEEP_VAR                  : SOP1_IMM_Real_gfx12<0x058>;
 
 //===----------------------------------------------------------------------===//

llvm/test/MC/AMDGPU/gfx11_unsupported.s

@@ -322,6 +322,9 @@ image_sample_cd_o v252, v[1:4], s[8:15], s[12:15] dmask:0x1
 image_sample_cd_o_g16 v[5:6], v[1:4], s[8:15], s[12:15] dmask:0x3
 // CHECK: :[[@LINE-1]]:{{[0-9]+}}: error: instruction not supported on this GPU
 
+s_alloc_vgpr s0
+// CHECK: :[[@LINE-1]]:{{[0-9]+}}: error: instruction not supported on this GPU
+
 s_atomic_add flat_scratch_hi, s[2:3], s0
 // CHECK: :[[@LINE-1]]:{{[0-9]+}}: error: instruction not supported on this GPU
 

llvm/test/MC/AMDGPU/gfx12_asm_sop1.s

@@ -1,5 +1,14 @@
 // RUN: llvm-mc -triple=amdgcn -show-encoding -mcpu=gfx1200 %s | FileCheck --check-prefix=GFX12 %s
 
+s_alloc_vgpr 0x1235
+// GFX12: encoding: [0xff,0x53,0x80,0xbe,0x35,0x12,0x00,0x00]
+
+s_alloc_vgpr 18
+// GFX12: encoding: [0x92,0x53,0x80,0xbe]
+
+s_alloc_vgpr s35
+// GFX12: encoding: [0x23,0x53,0x80,0xbe]
+
 s_sleep_var 0x1234
 // GFX12: encoding: [0xff,0x58,0x80,0xbe,0x34,0x12,0x00,0x00]
 

llvm/test/MC/Disassembler/AMDGPU/gfx12_dasm_sop1.txt

@@ -1,5 +1,14 @@
 # RUN: llvm-mc -triple=amdgcn -mcpu=gfx1200 -disassemble -show-encoding < %s | FileCheck -check-prefixes=GFX12 %s
 
+# GFX12: s_alloc_vgpr 0x1235                          ; encoding: [0xff,0x53,0x80,0xbe,0x35,0x12,0x00,0x00]
+0xff,0x53,0x80,0xbe,0x35,0x12,0x00,0x00
+
+# GFX12: s_alloc_vgpr 18                              ; encoding: [0x92,0x53,0x80,0xbe]
+0x92,0x53,0x80,0xbe
+
+# GFX12: s_alloc_vgpr s35                             ; encoding: [0x23,0x53,0x80,0xbe]
+0x23,0x53,0x80,0xbe
+
 # GFX12: s_sleep_var 0x1234                   ; encoding: [0xff,0x58,0x80,0xbe,0x34,0x12,0x00,0x00]
 0xff,0x58,0x80,0xbe,0x34,0x12,0x00,0x00