v3d: adds an extra MOV for any sig.ld*

Specifically when we are in non-uniform control flow, as we would need
to set the condition for the last instruction. If (for example) a
image atomic load stores directly their value on a NIR register,
last_inst would be a nop, and would fail when set the condition.

Fixes piglit test:
spec/glsl-es-3.10/execution/cs-ssbo-atomic-if-else-2.shader_test

Fixes: 6281f26f06 ("v3d: Add support for shader_image_load_store.")

v2: (Changes suggested by Eric Anholt)
   * Cover all sig.ld* signals, not just ldunif and ldtmu, as all of
     them have the same restriction.
   * Update comment explaining why we add a MOV in that case
   * Tweak commit message.

v3:
   * Drop extra set of parens (Eric)
   * Add missing ld signal to is_ld_signal to fix shader-db regression.

Reviewed-by: Eric Anholt <eric@anholt.net>

src/broadcom/compiler/nir_to_vir.c

@@ -409,6 +409,20 @@ ntq_init_ssa_def(struct v3d_compile *c, nir_ssa_def *def)
         return qregs;
 }
 
+static bool
+is_ld_signal(const struct v3d_qpu_sig *sig)
+{
+        return (sig->ldunif ||
+                sig->ldunifa ||
+                sig->ldunifrf ||
+                sig->ldunifarf ||
+                sig->ldtmu ||
+                sig->ldvary ||
+                sig->ldvpm ||
+                sig->ldtlb ||
+                sig->ldtlbu);
+}
+
 /**
  * This function is responsible for getting VIR results into the associated
  * storage for a NIR instruction.
@@ -456,11 +470,12 @@ ntq_store_dest(struct v3d_compile *c, nir_dest *dest, int chan,
                         _mesa_hash_table_search(c->def_ht, reg);
                 struct qreg *qregs = entry->data;
 
-                /* Insert a MOV if the source wasn't an SSA def in the
-                 * previous instruction.
+                /* If the previous instruction can't be predicated for
+                 * the store into the nir_register, then emit a MOV
+                 * that can be.
                  */
-                if ((vir_in_nonuniform_control_flow(c) &&
-                     c->defs[last_inst->dst.index]->qpu.sig.ldunif)) {
+                if (vir_in_nonuniform_control_flow(c) &&
+                    is_ld_signal(&c->defs[last_inst->dst.index]->qpu.sig)) {
                         result = vir_MOV(c, result);
                         last_inst = c->defs[result.index];
                 }