[AMDGPU] Add GFX12 S_ALLOC_VGPR instruction

[rovka]

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.

[llvmbot]

@llvm/pr-subscribers-mc

@llvm/pr-subscribers-backend-amdgpu

Author: Diana Picus (rovka)

Changes

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.

---

Full diff: https://github.com/llvm/llvm-project/pull/130018.diff

4 Files Affected:

• (modified) llvm/lib/Target/AMDGPU/SOPInstructions.td (+7)
• (modified) llvm/test/MC/AMDGPU/gfx11_unsupported.s (+3)
• (modified) llvm/test/MC/AMDGPU/gfx12_asm_sop1.s (+9)
• (modified) llvm/test/MC/Disassembler/AMDGPU/gfx12_dasm_sop1.txt (+9)

diff --git a/llvm/lib/Target/AMDGPU/SOPInstructions.td b/llvm/lib/Target/AMDGPU/SOPInstructions.td
index 5e62ceac281b8..eeac9c1ad1084 100644
--- a/llvm/lib/Target/AMDGPU/SOPInstructions.td
+++ b/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>;
 
 //===----------------------------------------------------------------------===//
diff --git a/llvm/test/MC/AMDGPU/gfx11_unsupported.s b/llvm/test/MC/AMDGPU/gfx11_unsupported.s
index d5d10ce548c4d..cd30647fe6378 100644
--- a/llvm/test/MC/AMDGPU/gfx11_unsupported.s
+++ b/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
 
diff --git a/llvm/test/MC/AMDGPU/gfx12_asm_sop1.s b/llvm/test/MC/AMDGPU/gfx12_asm_sop1.s
index 1e12e5bb48828..3828a4d36adcc 100644
--- a/llvm/test/MC/AMDGPU/gfx12_asm_sop1.s
+++ b/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]
 
diff --git a/llvm/test/MC/Disassembler/AMDGPU/gfx12_dasm_sop1.txt b/llvm/test/MC/Disassembler/AMDGPU/gfx12_dasm_sop1.txt
index fa7d020bdd726..2ee84fa976d79 100644
--- a/llvm/test/MC/Disassembler/AMDGPU/gfx12_dasm_sop1.txt
+++ b/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
 

[arsenm]

Does this need error tests for VGPRs, or the exotic scalar registers?

[rovka]

Done. I'm not sure which ones are the exotic SGPRs, I added tests for m0, scc, vcc and exec. We don't accept the last 2 (although I think sp3 accepts all of them).