Mesa (master): ac/llvm: implement 16-bit and 64-bit fpow correctly

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Module: Mesa
Branch: master
Commit: 46ce67a3310220e346382760a07269224b8d74fb
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=46ce67a3310220e346382760a07269224b8d74fb

Author: Marek Olšák <marek.olsak at amd.com>
Date:   Fri Feb 12 01:05:19 2021 -0500

ac/llvm: implement 16-bit and 64-bit fpow correctly

LLVM converts to 32 bits and back for llvm.pow, so we can't use it.

Acked-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer at amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9395>

---

 src/amd/llvm/ac_nir_to_llvm.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/amd/llvm/ac_nir_to_llvm.c b/src/amd/llvm/ac_nir_to_llvm.c
index a70eb0a64b0..50542687966 100644
--- a/src/amd/llvm/ac_nir_to_llvm.c
+++ b/src/amd/llvm/ac_nir_to_llvm.c
@@ -843,6 +843,15 @@ static void visit_alu(struct ac_nir_context *ctx, const nir_alu_instr *instr)
       result = ac_build_frexp_mant(&ctx->ac, src[0], instr->dest.dest.ssa.bit_size);
       break;
    case nir_op_fpow:
+      if (instr->dest.dest.ssa.bit_size != 32) {
+         /* 16 and 64 bits */
+         result = emit_intrin_1f_param(&ctx->ac, "llvm.log2",
+                                       ac_to_float_type(&ctx->ac, def_type), src[0]);
+         result = LLVMBuildFMul(ctx->ac.builder, result, ac_to_float(&ctx->ac, src[1]), "");
+         result = emit_intrin_1f_param(&ctx->ac, "llvm.exp2",
+                                       ac_to_float_type(&ctx->ac, def_type), result);
+         break;
+      }
       result = emit_intrin_2f_param(&ctx->ac, "llvm.pow", ac_to_float_type(&ctx->ac, def_type),
                                     src[0], src[1]);
       break;