agx: Add break_if_*cmp instructions

To faciliate break optimizations. We use a more efficient lowering than the
literal transition of the NIR.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25052>

src/asahi/compiler/agx_lower_pseudo.c

@@ -8,6 +8,42 @@
 #include "agx_opcodes.h"
 
 /* Lower pseudo instructions created during optimization. */
+
+static agx_instr *
+while_for_break_if(agx_builder *b, agx_instr *I)
+{
+   if (I->op == AGX_OPCODE_BREAK_IF_FCMP) {
+      return agx_while_fcmp(b, I->src[0], I->src[1], I->nest, I->fcond,
+                            !I->invert_cond);
+   } else {
+      return agx_while_icmp(b, I->src[0], I->src[1], I->nest, I->icond,
+                            !I->invert_cond);
+   }
+}
+
+static agx_instr *
+cmpsel_for_break_if(agx_builder *b, agx_instr *I)
+{
+   agx_index r0l = agx_register(0, AGX_SIZE_16);
+
+   /* If the condition is true, set r0l to nest to break */
+   agx_index t = agx_immediate(I->nest);
+   agx_index f = r0l;
+
+   if (I->invert_cond) {
+      agx_index temp = t;
+      t = f;
+      f = temp;
+   }
+
+   if (I->op == AGX_OPCODE_BREAK_IF_FCMP)
+      agx_fcmpsel_to(b, r0l, I->src[0], I->src[1], t, f, I->fcond);
+   else
+      agx_icmpsel_to(b, r0l, I->src[0], I->src[1], t, f, I->icond);
+
+   return agx_push_exec(b, 0);
+}
+
 static agx_instr *
 lower(agx_builder *b, agx_instr *I)
 {
@@ -37,6 +73,14 @@ lower(agx_builder *b, agx_instr *I)
       agx_mov_imm_to(b, agx_register(0, AGX_SIZE_16), I->nest);
       return agx_pop_exec(b, 0);
 
+   case AGX_OPCODE_BREAK_IF_ICMP:
+   case AGX_OPCODE_BREAK_IF_FCMP: {
+      if (I->nest == 1)
+         return while_for_break_if(b, I);
+      else
+         return cmpsel_for_break_if(b, I);
+   }
+
    default:
       return NULL;
    }

src/asahi/compiler/agx_opcodes.py

@@ -424,3 +424,8 @@ op("preload", _, srcs = 1, schedule_class = "preload")
 op("begin_cf", _, dests = 0, can_eliminate = False)
 op("break", _, dests = 0, imms = [NEST], can_eliminate = False,
    schedule_class = "invalid")
+
+for (name, is_float) in [("break_if_icmp", False), ("break_if_fcmp", True)]:
+    op(name, _, dests = 0, srcs = 2,
+       imms = [NEST, INVERT_COND, FCOND if is_float else ICOND],
+       can_eliminate = False, schedule_class = "invalid")