AMDGPU: llvm.amdgcn.inverse.ballot needs to be convergent (#155725)

It is only defined for uniform inputs (instruction selection inserts
v_readfirstlane as necessary).

Author: nhaehnle

llvm/include/llvm/IR/IntrinsicsAMDGPU.td

@@ -2434,9 +2434,13 @@ def int_amdgcn_ballot :
   Intrinsic<[llvm_anyint_ty], [llvm_i1_ty],
             [IntrNoMem, IntrConvergent, IntrWillReturn, IntrNoCallback, IntrNoFree]>;
 
+// Inverse of ballot: return the bit corresponding to the current lane from the
+// given mask.
+//
+// This is only defined for dynamically uniform masks and therefore convergent.
 def int_amdgcn_inverse_ballot :
   Intrinsic<[llvm_i1_ty], [llvm_anyint_ty],
-            [IntrNoMem, IntrWillReturn, IntrNoCallback, IntrNoFree]>;
+            [IntrNoMem, IntrConvergent, IntrWillReturn, IntrNoCallback, IntrNoFree]>;
 
 // Lowers to S_BITREPLICATE_B64_B32.
 // The argument must be uniform; otherwise, the result is undefined.

llvm/test/CodeGen/AMDGPU/llvm.amdgcn.inverse.ballot.i32.ll

@@ -5,7 +5,7 @@
 ; RUN: not llc -mtriple=amdgcn -mcpu=gfx1100 -mattr=+wavefrontsize64 -global-isel=1 < %s 2>&1 | FileCheck  -check-prefix=GISEL-ERR %s
 ; RUN: not --crash llc -mtriple=amdgcn -mcpu=gfx1100 -mattr=+wavefrontsize64 -global-isel=0 < %s 2>&1 | FileCheck  -check-prefix=SDAG-ERR %s
 
-; GISEL-ERR: LLVM ERROR: cannot select: {{.*}}  = G_INTRINSIC intrinsic(@llvm.amdgcn.inverse.ballot)
+; GISEL-ERR: LLVM ERROR: cannot select: {{.*}}  = G_INTRINSIC_CONVERGENT intrinsic(@llvm.amdgcn.inverse.ballot)
 ; SDAG-ERR: LLVM ERROR: Cannot select: intrinsic %llvm.amdgcn.inverse.ballot
 
 declare i1 @llvm.amdgcn.inverse.ballot(i32)