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aco/isel: Fix large inputs being truncated in int32->f16 conversions

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The previous code produced incorrect results for inputs outside the
range [INT16_MIN, INT16_MAX].

A problematic case is e.g. i2f16 32768, which previously would be
converted to -32768.0 instead of returning the exactly representable
floating point result.

Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9597>
This commit is contained in:
Tony Wasserka 2021-03-16 10:52:39 +01:00 • committed by Marge Bot
parent 4ce8e422e3
commit b5be03f39f
1 changed files with 11 additions and 2 deletions
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13
src/amd/compiler/aco_instruction_selection.cpp
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@ -2453,10 +2453,17 @@ void visit_alu_instr(isel_context *ctx, nir_alu_instr *instr)
src = convert_int(ctx, bld, src, 64, 32, false);
}
if (ctx->program->chip_class >= GFX8) {
if (ctx->program->chip_class >= GFX8 && input_size <= 16) {
bld.vop1(aco_opcode::v_cvt_f16_i16, Definition(dst), src);
} else {
/* GFX7 and earlier do not support direct f16⟷i16 conversions */
/* Convert to f32 and then down to f16. This is needed to handle
* inputs slightly outside the range [INT16_MIN, INT16_MAX],
* which are representable via f16 but wouldn't be converted
* correctly by v_cvt_f16_i16.
*
* This is also the fallback-path taken on GFX7 and earlier, which
* do not support direct f16⟷i16 conversions.
*/
src = bld.vop1(aco_opcode::v_cvt_f32_i32, bld.def(v1), src);
bld.vop1(aco_opcode::v_cvt_f16_f32, Definition(dst), src);
}
@ -2522,6 +2529,8 @@ void visit_alu_instr(isel_context *ctx, nir_alu_instr *instr)
}
if (ctx->program->chip_class >= GFX8) {
/* float16 has a range of [0, 65519]. Converting from larger
* inputs is UB, so we just need to consider the lower 16 bits */
bld.vop1(aco_opcode::v_cvt_f16_u16, Definition(dst), src);
} else {
/* GFX7 and earlier do not support direct f16⟷u16 conversions */