ir3: fold negations into cmps.ne zero

It was already implemented for sel so pull that functionality into a
helper function which can be used from ir3_get_predicate.

Signed-off-by: Job Noorman <jnoorman@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27411>

src/freedreno/ir3/ir3.c

@@ -1297,3 +1297,18 @@ ir3_valid_immediate(struct ir3_instruction *instr, int32_t immed)
    /* Other than cat1 (mov) we can only encode up to 10 bits, sign-extended: */
    return !(immed & ~0x1ff) || !(-immed & ~0x1ff);
 }
+
+struct ir3_instruction *
+ir3_get_cond_for_nonzero_compare(struct ir3_instruction *instr)
+{
+   /* If instr is a negation (likely as a result of an nir_b2n), we can ignore
+    * that and use its source, since the nonzero-ness stays the same.
+    */
+   if (instr->opc == OPC_ABSNEG_S && instr->flags == 0 &&
+       (instr->srcs[0]->flags & (IR3_REG_SNEG | IR3_REG_SABS)) ==
+          IR3_REG_SNEG) {
+      return instr->srcs[0]->def->instr;
+   }
+
+   return instr;
+}

src/freedreno/ir3/ir3.h

@@ -844,6 +844,14 @@ bool ir3_valid_flags(struct ir3_instruction *instr, unsigned n, unsigned flags);
 
 bool ir3_valid_immediate(struct ir3_instruction *instr, int32_t immed);
 
+/**
+ * Given an instruction whose result we want to test for nonzero, return a
+ * potentially different instruction for which the result would be the same.
+ * This might be one of its sources if instr doesn't change the nonzero-ness.
+ */
+struct ir3_instruction *
+ir3_get_cond_for_nonzero_compare(struct ir3_instruction *instr);
+
 #include "util/set.h"
 #define foreach_ssa_use(__use, __instr)                                        \
    for (struct ir3_instruction *__use = (void *)~0; __use && (__instr)->uses;  \

src/freedreno/ir3/ir3_compiler_nir.c

@@ -712,17 +712,7 @@ emit_alu(struct ir3_context *ctx, nir_alu_instr *alu)
       break;
 
    case nir_op_bcsel: {
-      struct ir3_instruction *cond = src[0];
-
-      /* If src[0] is a negation (likely as a result of an ir3_b2n(cond)),
-       * we can ignore that and use original cond, since the nonzero-ness of
-       * cond stays the same.
-       */
-      if (cond->opc == OPC_ABSNEG_S && cond->flags == 0 &&
-          (cond->srcs[0]->flags & (IR3_REG_SNEG | IR3_REG_SABS)) ==
-             IR3_REG_SNEG) {
-         cond = cond->srcs[0]->def->instr;
-      }
+      struct ir3_instruction *cond = ir3_get_cond_for_nonzero_compare(src[0]);
 
       compile_assert(ctx, bs[1] == bs[2]);
 

src/freedreno/ir3/ir3_context.c

@@ -461,6 +461,8 @@ ir3_get_addr1(struct ir3_context *ctx, unsigned const_val)
 struct ir3_instruction *
 ir3_get_predicate(struct ir3_context *ctx, struct ir3_instruction *src)
 {
+   src = ir3_get_cond_for_nonzero_compare(src);
+
    struct hash_entry *src_entry =
       _mesa_hash_table_search(ctx->predicate_conversions, src);
    if (src_entry)