Mesa (master): aco: fix 64-bit trunc with negative exponents on GFX6

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Module: Mesa
Branch: master
Commit: 3fba0a7a6f01496344ddb93e774b2d4bc9195e8a
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=3fba0a7a6f01496344ddb93e774b2d4bc9195e8a

Author: Samuel Pitoiset <samuel.pitoiset at gmail.com>
Date:   Wed May  6 15:34:07 2020 +0200

aco: fix 64-bit trunc with negative exponents on GFX6

v_frexp_exp returns the exponent as an unsigned value.

Also, v_ashr returns either 0 or -1 depending on the sign of the
source operand, but what we want is only the sign bit.

Fixes a bunch of recent dEQP-VK.glsl.builtin.precision_double.* tests.

Cc: <mesa-stable at lists.freedesktop.org>
Signed-off-by: Samuel Pitoiset <samuel.pitoiset at gmail.com>
Reviewed-by: Daniel Schürmann <daniel at schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4921>

---

 src/amd/compiler/aco_instruction_selection.cpp | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/amd/compiler/aco_instruction_selection.cpp b/src/amd/compiler/aco_instruction_selection.cpp
index 1ac3cda14a8..65cf38f57e9 100644
--- a/src/amd/compiler/aco_instruction_selection.cpp
+++ b/src/amd/compiler/aco_instruction_selection.cpp
@@ -878,7 +878,8 @@ Temp emit_trunc_f64(isel_context *ctx, Builder& bld, Definition dst, Temp val)
    bld.pseudo(aco_opcode::p_split_vector, Definition(val_lo), Definition(val_hi), val);
 
    /* Extract the exponent and compute the unbiased value. */
-   Temp exponent = bld.vop1(aco_opcode::v_frexp_exp_i32_f64, bld.def(v1), val);
+   Temp exponent = bld.vop3(aco_opcode::v_bfe_u32, bld.def(v1), val_hi, Operand(20u), Operand(11u));
+   exponent = bld.vsub32(bld.def(v1), exponent, Operand(1023u));
 
    /* Extract the fractional part. */
    Temp fract_mask = bld.pseudo(aco_opcode::p_create_vector, bld.def(v2), Operand(-1u), Operand(0x000fffffu));
@@ -894,7 +895,7 @@ Temp emit_trunc_f64(isel_context *ctx, Builder& bld, Definition dst, Temp val)
    fract_hi = bld.vop2(aco_opcode::v_and_b32, bld.def(v1), val_hi, tmp);
 
    /* Get the sign bit. */
-   Temp sign = bld.vop2(aco_opcode::v_ashr_i32, bld.def(v1), Operand(31u), val_hi);
+   Temp sign = bld.vop2(aco_opcode::v_and_b32, bld.def(v1), Operand(0x80000000u), val_hi);
 
    /* Decide the operation to apply depending on the unbiased exponent. */
    Temp exp_lt0 = bld.vopc_e64(aco_opcode::v_cmp_lt_i32, bld.hint_vcc(bld.def(bld.lm)), exponent, Operand(0u));