Mesa (main): nir: Fix idiv lowering on !NativeIntegers when lower_fdiv is also set.

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Module: Mesa
Branch: main
Commit: 5c499d6d1adfb9c90b672ff7124ffbf5b4bdf56f
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=5c499d6d1adfb9c90b672ff7124ffbf5b4bdf56f

Author: Emma Anholt <emma at anholt.net>
Date:   Mon Jun  6 11:30:51 2022 -0700

nir: Fix idiv lowering on !NativeIntegers when lower_fdiv is also set.

Avoids a regression when turning off GLSL's int div lowering.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16823>

---

 src/compiler/nir/nir_lower_int_to_float.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/compiler/nir/nir_lower_int_to_float.c b/src/compiler/nir/nir_lower_int_to_float.c
index f7fa55ac3b2..6cdb53e7768 100644
--- a/src/compiler/nir/nir_lower_int_to_float.c
+++ b/src/compiler/nir/nir_lower_int_to_float.c
@@ -101,11 +101,20 @@ lower_alu_instr(nir_builder *b, nir_alu_instr *alu)
    case nir_op_iadd: alu->op = nir_op_fadd; break;
    case nir_op_isub: alu->op = nir_op_fsub; break;
    case nir_op_imul: alu->op = nir_op_fmul; break;
-   case nir_op_idiv:
-      rep = nir_ftrunc(b, nir_fdiv(b,
-                                   nir_ssa_for_alu_src(b, alu, 0),
-                                   nir_ssa_for_alu_src(b, alu, 1)));
+
+   case nir_op_idiv: {
+      nir_ssa_def *x = nir_ssa_for_alu_src(b, alu, 0);
+      nir_ssa_def *y = nir_ssa_for_alu_src(b, alu, 1);
+
+      /* Hand-lower fdiv, since lower_int_to_float is after nir_opt_algebraic. */
+      if (b->shader->options->lower_fdiv) {
+         rep = nir_ftrunc(b, nir_fmul(b, x, nir_frcp(b, y)));
+      } else {
+         rep = nir_ftrunc(b, nir_fdiv(b, x, y));
+      }
       break;
+   }
+
    case nir_op_iabs: alu->op = nir_op_fabs; break;
    case nir_op_ineg: alu->op = nir_op_fneg; break;
    case nir_op_imax: alu->op = nir_op_fmax; break;