nir/search: Add support for matching unknown constants

There are some algebraic transformations that we want to do but only if
certain things are constants.  For instance, we may want to replace
a * (b + c) with (a * b) + (a * c) as long as a and either b or c is constant.
While this generates more instructions, some of it will get constant
folded.

nir_algebraic.py doesn't handle this yet, but that's ok because the C
language will make sure that false is the default for now.

Reviewed-by: Kenneth Graunke <[email protected]>

1 files changed, 6 insertions, 0 deletions

diff --git a/src/glsl/nir/nir_search.c b/src/glsl/nir/nir_search.c
index 18e0330e4ae..ec898174364 100644
--- a/src/glsl/nir/nir_search.c
+++ b/src/glsl/nir/nir_search.c
@@ -78,6 +78,10 @@ match_value(const nir_search_value *value, nir_alu_instr *instr, unsigned src,
 
          return true;
       } else {
+         if (var->is_constant &&
+             instr->src[src].src.ssa->parent_instr->type != nir_instr_type_load_const)
+            return false;
+
          state->variables_seen |= (1 << var->variable);
          state->variables[var->variable].src = instr->src[src].src;
          state->variables[var->variable].abs = false;
@@ -236,6 +240,8 @@ construct_value(const nir_search_value *value, nir_alu_type type,
       nir_alu_src val;
       nir_alu_src_copy(&val, &state->variables[var->variable], mem_ctx);
 
+      assert(!var->is_constant);
+
       return val;
    }