From 2c2aaf275c1edba38c552ac74de4d46bb2ebfbe8 Mon Sep 17 00:00:00 2001 From: Samuel Pitoiset Date: Mon, 14 Oct 2019 15:39:06 +0200 Subject: [PATCH] ac/llvm: force fneg/fabs to flush denorms to zero if requested LLVM optimizes these instructions with XOR/AND and it loses the sign bit. Signed-off-by: Samuel Pitoiset Reviewed-by: Bas Nieuwenhuizen --- src/amd/llvm/ac_nir_to_llvm.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/src/amd/llvm/ac_nir_to_llvm.c b/src/amd/llvm/ac_nir_to_llvm.c index ab042d36083..cd7091ad163 100644 --- a/src/amd/llvm/ac_nir_to_llvm.c +++ b/src/amd/llvm/ac_nir_to_llvm.c @@ -516,6 +516,13 @@ static void visit_alu(struct ac_nir_context *ctx, const nir_alu_instr *instr) case nir_op_fneg: src[0] = ac_to_float(&ctx->ac, src[0]); result = LLVMBuildFNeg(ctx->ac.builder, src[0], ""); + if (ctx->ac.float_mode == AC_FLOAT_MODE_DENORM_FLUSH_TO_ZERO) { + /* fneg will be optimized by backend compiler with sign + * bit removed via XOR. This is probably a LLVM bug. + */ + result = ac_build_canonicalize(&ctx->ac, result, + instr->dest.dest.ssa.bit_size); + } break; case nir_op_ineg: result = LLVMBuildNeg(ctx->ac.builder, src[0], ""); @@ -646,6 +653,13 @@ static void visit_alu(struct ac_nir_context *ctx, const nir_alu_instr *instr) case nir_op_fabs: result = emit_intrin_1f_param(&ctx->ac, "llvm.fabs", ac_to_float_type(&ctx->ac, def_type), src[0]); + if (ctx->ac.float_mode == AC_FLOAT_MODE_DENORM_FLUSH_TO_ZERO) { + /* fabs will be optimized by backend compiler with sign + * bit removed via AND. + */ + result = ac_build_canonicalize(&ctx->ac, result, + instr->dest.dest.ssa.bit_size); + } break; case nir_op_iabs: result = emit_iabs(&ctx->ac, src[0]); -- 2.30.2