[Mesa-dev] [PATCH] 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-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 32-bit. This adds an optional conversion of the final argument in
order to support either 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
---
 src/compiler/spirv/vtn_glsl450.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/compiler/spirv/vtn_glsl450.c b/src/compiler/spirv/vtn_glsl450.c
index 46ef40f5e3f..b098f082f3e 100644
--- a/src/compiler/spirv/vtn_glsl450.c
+++ b/src/compiler/spirv/vtn_glsl450.c
@@ -583,14 +583,14 @@ 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;
@@ -600,8 +600,17 @@ 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)
+         eta = nir_build_alu(nb, nir_op_f2f64, 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