From 8a995f2b5e1e3f2a2eafd32870ebfb43b5cfdf27 Mon Sep 17 00:00:00 2001 From: Caio Marcelo de Oliveira Filho Date: Sat, 11 May 2019 00:15:41 -0700 Subject: [PATCH] nir: Fix nir_opt_idiv_const when negatives are involved First, allow the case for negative powers of two. Then ensure that we use the absolute value of the non-constant value to calculate the quotient -- this was hinted in the code by the name 'uq'. This fixes an issue when 'd' is positive and 'n' is negative. The ishr will propagate the negative sign and we'll use nir_ineg() again, incorrectly. v2: First version used only ishr, but that isn't sufficient, since it never can produce a zero as a result. (Jason) Allow negative powers of two. (Caio) Fixes: 74492ebad94 "nir: Add a pass for lowering integer division by constants" Reviewed-by: Jason Ekstrand --- src/compiler/nir/nir_opt_idiv_const.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/src/compiler/nir/nir_opt_idiv_const.c b/src/compiler/nir/nir_opt_idiv_const.c index 8f70821ca2f..688186779e6 100644 --- a/src/compiler/nir/nir_opt_idiv_const.c +++ b/src/compiler/nir/nir_opt_idiv_const.c @@ -65,15 +65,17 @@ build_umod(nir_builder *b, nir_ssa_def *n, uint64_t d) static nir_ssa_def * build_idiv(nir_builder *b, nir_ssa_def *n, int64_t d) { + uint64_t abs_d = d < 0 ? -d : d; + if (d == 0) { return nir_imm_intN_t(b, 0, n->bit_size); } else if (d == 1) { return n; } else if (d == -1) { return nir_ineg(b, n); - } else if (util_is_power_of_two_or_zero64(d)) { - uint64_t abs_d = d < 0 ? -d : d; - nir_ssa_def *uq = nir_ishr(b, n, nir_imm_int(b, util_logbase2_64(abs_d))); + } else if (util_is_power_of_two_or_zero64(abs_d)) { + nir_ssa_def *uq = nir_ushr(b, nir_iabs(b, n), + nir_imm_int(b, util_logbase2_64(abs_d))); nir_ssa_def *n_neg = nir_ilt(b, n, nir_imm_intN_t(b, 0, n->bit_size)); nir_ssa_def *neg = d < 0 ? nir_inot(b, n_neg) : n_neg; return nir_bcsel(b, neg, nir_ineg(b, uq), uq); -- 2.30.2