Mesa (main): spirv: Produce correct result for GLSLstd450Modf with Inf

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Module: Mesa
Branch: main
Commit: e442b9d79296ad9322af61fdadbc81d680466f57
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=e442b9d79296ad9322af61fdadbc81d680466f57

Author: Ian Romanick <ian.d.romanick at intel.com>
Date:   Fri Oct 29 08:15:18 2021 -0700

spirv: Produce correct result for GLSLstd450Modf with Inf

GLSLstd450ModfStruct too.

No shader-db or fossil-db changes on any Intel platform.

v2: Fix handling 16-bit (and presumably 64-bit) values.

Reviewed-by: Caio Oliveira <caio.oliveira at intel.com>
Fixes: f92a35d831c ("vtn: Fix Modf.")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13999>

---

 src/compiler/spirv/vtn_glsl450.c | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/src/compiler/spirv/vtn_glsl450.c b/src/compiler/spirv/vtn_glsl450.c
index d596c251548..21f5fa80973 100644
--- a/src/compiler/spirv/vtn_glsl450.c
+++ b/src/compiler/spirv/vtn_glsl450.c
@@ -332,9 +332,22 @@ handle_glsl450_alu(struct vtn_builder *b, enum GLSLstd450 entrypoint,
       break;
 
    case GLSLstd450Modf: {
+      nir_ssa_def *inf = nir_imm_floatN_t(&b->nb, INFINITY, src[0]->bit_size);
+      nir_ssa_def *sign_bit =
+         nir_imm_intN_t(&b->nb, (uint64_t)1 << (src[0]->bit_size - 1),
+                        src[0]->bit_size);
       nir_ssa_def *sign = nir_fsign(nb, src[0]);
       nir_ssa_def *abs = nir_fabs(nb, src[0]);
-      dest->def = nir_fmul(nb, sign, nir_ffract(nb, abs));
+
+      /* NaN input should produce a NaN results, and ±Inf input should provide
+       * ±0 result.  The fmul(sign(x), ffract(x)) calculation will already
+       * produce the expected NaN.  To get ±0, directly compare for equality
+       * with Inf instead of using fisfinite (which is false for NaN).
+       */
+      dest->def = nir_bcsel(nb,
+                            nir_ieq(nb, abs, inf),
+                            nir_iand(nb, src[0], sign_bit),
+                            nir_fmul(nb, sign, nir_ffract(nb, abs)));
 
       struct vtn_pointer *i_ptr = vtn_value(b, w[6], vtn_value_type_pointer)->pointer;
       struct vtn_ssa_value *whole = vtn_create_ssa_value(b, i_ptr->type->type);
@@ -344,10 +357,19 @@ handle_glsl450_alu(struct vtn_builder *b, enum GLSLstd450 entrypoint,
    }
 
    case GLSLstd450ModfStruct: {
+      nir_ssa_def *inf = nir_imm_floatN_t(&b->nb, INFINITY, src[0]->bit_size);
+      nir_ssa_def *sign_bit =
+         nir_imm_intN_t(&b->nb, (uint64_t)1 << (src[0]->bit_size - 1),
+                        src[0]->bit_size);
       nir_ssa_def *sign = nir_fsign(nb, src[0]);
       nir_ssa_def *abs = nir_fabs(nb, src[0]);
       vtn_assert(glsl_type_is_struct_or_ifc(dest_type));
-      dest->elems[0]->def = nir_fmul(nb, sign, nir_ffract(nb, abs));
+
+      /* See GLSLstd450Modf for explanation of the Inf and NaN handling. */
+      dest->elems[0]->def = nir_bcsel(nb,
+                                      nir_ieq(nb, abs, inf),
+                                      nir_iand(nb, src[0], sign_bit),
+                                      nir_fmul(nb, sign, nir_ffract(nb, abs)));
       dest->elems[1]->def = nir_fmul(nb, sign, nir_ffloor(nb, abs));
       break;
    }