Add test for what happens when you violate the attribute

We hit the allocation error, but we probably should treat it as UB and only
emit a warning.

Author: arsenm

llvm/test/CodeGen/AMDGPU/amdgpu-no-agprs-violations.ll

@@ -0,0 +1,50 @@
+; RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx908 < %s | FileCheck -check-prefixes=CHECK,GFX908 %s
+; RUN: not llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx90a < %s 2> %t.err | FileCheck -check-prefixes=CHECK,GFX90A %s
+; RUN: FileCheck -check-prefix=ERR < %t.err %s
+
+; Test undefined behavior where a function ends up needing AGPRs that
+; was marked with "amdgpu-num-agpr="="0". There should be no asserts.
+
+; TODO: Should this be an error, or let UB happen?
+
+; ERR: error: <unknown>:0:0: no registers from class available to allocate in function 'kernel_illegal_agpr_use_asm'
+; ERR: error: <unknown>:0:0: no registers from class available to allocate in function 'func_illegal_agpr_use_asm'
+; ERR: error: <unknown>:0:0: no registers from class available to allocate in function 'kernel_calls_mfma.f32.32x32x1f32'
+
+; CHECK: {{^}}kernel_illegal_agpr_use_asm:
+; CHECK: ; use a0
+
+; CHECK: NumVgprs: 0
+; CHECK: NumAgprs: 1
+define amdgpu_kernel void @kernel_illegal_agpr_use_asm() #0 {
+  call void asm sideeffect "; use $0", "a"(i32 poison)
+  ret void
+}
+
+; CHECK: {{^}}func_illegal_agpr_use_asm:
+; CHECK: ; use a0
+
+; CHECK: NumVgprs: 0
+; CHECK: NumAgprs: 1
+define void @func_illegal_agpr_use_asm() #0 {
+  call void asm sideeffect "; use $0", "a"(i32 poison)
+  ret void
+}
+
+; CHECK-LABEL: {{^}}kernel_calls_mfma.f32.32x32x1f32:
+; CHECK: v_accvgpr_write_b32
+; CHECK: v_accvgpr_read_b32
+
+; GFX908: NumVgprs: 5
+; GFX90A: NumVgprs: 36
+; CHECK: NumAgprs: 32
+
+; GFX908: TotalNumVgprs: 32
+; GFX90A: TotalNumVgprs: 68
+define amdgpu_kernel void @kernel_calls_mfma.f32.32x32x1f32(ptr addrspace(1) %out, float %a, float %b, <32 x float> %c) #0 {
+  %result = call <32 x float> @llvm.amdgcn.mfma.f32.32x32x1f32(float %a, float %b, <32 x float> %c, i32 0, i32 0, i32 0)
+  store <32 x float> %result, ptr addrspace(1) %out
+  ret void
+}
+
+attributes #0 = { "amdgpu-num-agpr"="0" }