nir/lower_tex: Update ->sampler_dim value before calling get_texture_size()

get_texture_size() will create a txs instruction with ->sampler_dim set
to the original tex->sampler_dim. The condition to call lower_rect()
only checks the value of ->sampler_dim and whether lower_rect is
requested or not. This leads to an infinite loop when calling
nir_lower_tex() with the same options until it returns false.

In order to avoid that, let's move the tex->sampler_dim patching before
get_texture_size() is called. This way the txs instruction will have
->sampler_dim set to GLSL_SAMPLER_DIM_2D and nir_lower_tex() won't try
to lower it on the subsequent passes.

Changes in v2:
* Add Jason R-b
* Add a comment explaining why we patch ->sampler_dim at the beginning
  of the lower_rect() func

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>

src/compiler/nir/nir_lower_tex.c

@@ -266,6 +266,11 @@ lower_offset(nir_builder *b, nir_tex_instr *tex)
 static void
 lower_rect(nir_builder *b, nir_tex_instr *tex)
 {
+   /* Set the sampler_dim to 2D here so that get_texture_size picks up the
+    * right dimensionality.
+    */
+   tex->sampler_dim = GLSL_SAMPLER_DIM_2D;
+
    nir_ssa_def *txs = get_texture_size(b, tex);
    nir_ssa_def *scale = nir_frcp(b, txs);
 
@@ -280,8 +285,6 @@ lower_rect(nir_builder *b, nir_tex_instr *tex)
                             &tex->src[i].src,
                             nir_src_for_ssa(nir_fmul(b, coords, scale)));
    }
-
-   tex->sampler_dim = GLSL_SAMPLER_DIM_2D;
 }
 
 static void