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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 <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
This commit is contained in:
Samuel Pitoiset 2019-10-14 15:39:06 +02:00
parent 7dfb15fff1
commit 2c2aaf275c
1 changed files with 14 additions and 0 deletions
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14
src/amd/llvm/ac_nir_to_llvm.c
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@ -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]);