[Mesa-dev] [PATCH v2 4/4] spirv: Accept doubles in FaceForward, Reflect and Refract

[Neil Roberts]

The SPIR-V spec doesn’t specify a size requirement for these and the
equivalent functions in the GLSL spec have explicit alternatives for
doubles. Refract is a little bit more complicated due to the fact that
the final argument is always supposed to be a scalar 32- or 16- bit
float regardless of the other operands. However in practice it seems
there is a bug in glslang that makes it convert the argument to 64-bit
if you actually try to pass it a 32-bit value while the other
arguments are 64-bit. This adds an optional conversion of the final
argument in order to support any type.

These have been tested against the automatically generated tests of
glsl-4.00/execution/built-in-functions using the ARB_gl_spirv branch
which tests it with quite a large range of combinations.

The issue with glslang has been filed here:
https://github.com/KhronosGroup/glslang/issues/1279

v2: Convert the eta operand of Refract from any size in order to make
    it eventually cope with 16-bit floats.
---
 src/compiler/spirv/vtn_glsl450.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/src/compiler/spirv/vtn_glsl450.c b/src/compiler/spirv/vtn_glsl450.c
index 50783fbfb4d..0cabedf741d 100644
--- a/src/compiler/spirv/vtn_glsl450.c
+++ b/src/compiler/spirv/vtn_glsl450.c
@@ -628,14 +628,14 @@ handle_glsl450_alu(struct vtn_builder *b, enum GLSLstd450 entrypoint,
    case GLSLstd450FaceForward:
       val->ssa->def =
          nir_bcsel(nb, nir_flt(nb, nir_fdot(nb, src[2], src[1]),
-                                   nir_imm_float(nb, 0.0)),
+                                   NIR_IMM_FP(nb, 0.0)),
                        src[0], nir_fneg(nb, src[0]));
       return;
 
    case GLSLstd450Reflect:
       /* I - 2 * dot(N, I) * N */
       val->ssa->def =
-         nir_fsub(nb, src[0], nir_fmul(nb, nir_imm_float(nb, 2.0),
+         nir_fsub(nb, src[0], nir_fmul(nb, NIR_IMM_FP(nb, 2.0),
                               nir_fmul(nb, nir_fdot(nb, src[0], src[1]),
                                            src[1])));
       return;
@@ -645,8 +645,22 @@ handle_glsl450_alu(struct vtn_builder *b, enum GLSLstd450 entrypoint,
       nir_ssa_def *N = src[1];
       nir_ssa_def *eta = src[2];
       nir_ssa_def *n_dot_i = nir_fdot(nb, N, I);
-      nir_ssa_def *one = nir_imm_float(nb, 1.0);
-      nir_ssa_def *zero = nir_imm_float(nb, 0.0);
+      nir_ssa_def *one = NIR_IMM_FP(nb, 1.0);
+      nir_ssa_def *zero = NIR_IMM_FP(nb, 0.0);
+      /* According to the SPIR-V and GLSL specs, eta is always a float
+       * regardless of the type of the other operands. However in practice it
+       * seems that if you try to pass it a float then glslang will just
+       * promote it to a double and generate invalid SPIR-V. In order to
+       * support a hypothetical fixed version of glslang we’ll promote eta to
+       * double if the other operands are double also.
+       */
+      if (I->bit_size != eta->bit_size) {
+         nir_op conversion_op =
+            nir_type_conversion_op(nir_type_float | eta->bit_size,
+                                   nir_type_float | I->bit_size,
+                                   nir_rounding_mode_undef);
+         eta = nir_build_alu(nb, conversion_op, eta, NULL, NULL, NULL);
+      }
       /* k = 1.0 - eta * eta * (1.0 - dot(N, I) * dot(N, I)) */
       nir_ssa_def *k =
          nir_fsub(nb, one, nir_fmul(nb, eta, nir_fmul(nb, eta,
-- 
2.14.3