vc4: Add support for emitting IF nodes.

XXX: Need to condition updates to non-SSA NIR values on the execute flags.
XXX: Need to update the uniform pointer on block changes

src/gallium/drivers/vc4/vc4_program.c

@@ -43,6 +43,8 @@
 
 static struct qreg
 ntq_get_src(struct vc4_compile *c, nir_src src, int i);
+static void
+ntq_emit_cf_list(struct vc4_compile *c, struct exec_list *list);
 
 static void
 resize_qreg_array(struct vc4_compile *c,
@@ -1654,10 +1656,69 @@ ntq_emit_intrinsic(struct vc4_compile *c, nir_intrinsic_instr *instr)
         }
 }
 
+/* Clears (activates) the execute flags for any channels whose jump target
+ * matches this block.
+ */
+static void
+ntq_activate_execute_for_block(struct vc4_compile *c, struct qblock *block)
+{
+        qir_SF(c, qir_SUB(c, c->execute, qir_uniform_ui(c, block->index)));
+        qir_MOV_cond(c, QPU_COND_ZS, c->execute, qir_uniform_ui(c, 0));
+}
+
 static void
 ntq_emit_if(struct vc4_compile *c, nir_if *if_stmt)
 {
-        fprintf(stderr, "general IF statements not handled.\n");
+        struct qblock *prev_block = c->cur_block;
+        struct qblock *then_block = qir_new_block(c);
+        struct qblock *else_block = qir_new_block(c);
+        struct qblock *after_block = qir_new_block(c);
+
+        if (c->execute.file == QFILE_NULL)
+                c->execute = qir_MOV(c, qir_uniform_ui(c, 0));
+
+        /* Set ZS for executing (execute == 0) and jumping (if->condition ==
+         * 0) channels, and then update execute flags for those to point to
+         * the ELSE block.
+         */
+        qir_SF(c, qir_AND(c,
+                          c->execute,
+                          ntq_get_src(c, if_stmt->condition, 0)));
+        qir_MOV_cond(c, QPU_COND_ZS, c->execute,
+                     qir_uniform_ui(c, else_block->index));
+
+        /* Jump to ELSE if nothing is active for THEN, otherwise fall
+         * through.
+         */
+        qir_SF(c, c->execute);
+        qir_BRANCH(c, QPU_COND_BRANCH_ALL_ZC);
+        qir_link_blocks(prev_block, else_block);
+        qir_link_blocks(prev_block, then_block);
+
+        /* Process the THEN block. */
+        c->cur_block = then_block;
+        ntq_emit_cf_list(c, &if_stmt->then_list);
+
+        /* Handle the end of the THEN block.  First, all currently active
+         * channels update their execute flags to point to ENDIF
+         */
+        qir_SF(c, c->execute);
+        qir_MOV_cond(c, QPU_COND_ZS, c->execute,
+                     qir_uniform_ui(c, after_block->index));
+
+        /* If everything points at ENDIF, then jump there immediately. */
+        qir_SF(c, qir_SUB(c, c->execute, qir_uniform_ui(c, after_block->index)));
+        qir_BRANCH(c, QPU_COND_BRANCH_ALL_ZS);
+        qir_link_blocks(then_block, after_block);
+        qir_link_blocks(then_block, else_block);
+
+        c->cur_block = else_block;
+        ntq_activate_execute_for_block(c, else_block);
+        ntq_emit_cf_list(c, &if_stmt->else_list);
+        qir_link_blocks(else_block, after_block);
+
+        c->cur_block = after_block;
+        ntq_activate_execute_for_block(c, after_block);
 }
 
 static void

src/gallium/drivers/vc4/vc4_qir.h

@@ -411,6 +411,12 @@ struct vc4_compile {
         uint32_t next_ubo_dst_offset;
 
         struct qreg line_x, point_x, point_y;
+
+        /* State for whether we're executing on each channel currently.  0 if
+         * yes, otherwise a block number + 1.
+         */
+        struct qreg execute;
+
         struct qreg discard;
 
         uint8_t vattr_sizes[8];
@@ -754,6 +760,22 @@ qir_VPM_WRITE(struct vc4_compile *c, struct qreg val)
         qir_MOV_dest(c, qir_reg(QFILE_VPM, 0), val);
 }
 
+static inline void
+qir_MOV_cond(struct vc4_compile *c, uint8_t cond,
+             struct qreg dest, struct qreg src)
+{
+        qir_MOV_dest(c, dest, src)->cond = cond;
+}
+
+static inline struct qinst *
+qir_BRANCH(struct vc4_compile *c, uint8_t cond)
+{
+        struct qinst *inst = qir_inst(QOP_BRANCH, c->undef, c->undef, c->undef);
+        inst->cond = cond;
+        qir_emit(c, inst);
+        return inst;
+}
+
 #define qir_for_each_block(c, block) \
         list_for_each_entry(struct qblock, block, &c->blocks, link)