ac/llvm: add option to clamp division by zero
Replace div(x) by min(div(x), FLT_MAX)) to avoid getting a NaN result
when x is 0.
A cheaper alternative would be to use legacy mult instructions but they're
not exposed by LLVM.
Cc: mesa-stable
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6259>
diff --git a/src/amd/llvm/ac_nir_to_llvm.c b/src/amd/llvm/ac_nir_to_llvm.c
index 1b6ef26..6dc155d 100644
--- a/src/amd/llvm/ac_nir_to_llvm.c
+++ b/src/amd/llvm/ac_nir_to_llvm.c
@@ -713,6 +713,9 @@
result = emit_intrin_1f_param(&ctx->ac, "llvm.amdgcn.rcp",
ac_to_float_type(&ctx->ac, def_type), src[0]);
}
+ if (ctx->abi->clamp_div_by_zero)
+ result = ac_build_fmin(&ctx->ac, result,
+ LLVMConstReal(ac_to_float_type(&ctx->ac, def_type), FLT_MAX));
break;
case nir_op_iand:
result = LLVMBuildAnd(ctx->ac.builder, src[0], src[1], "");
@@ -859,6 +862,9 @@
case nir_op_frsq:
result = emit_intrin_1f_param(&ctx->ac, "llvm.amdgcn.rsq",
ac_to_float_type(&ctx->ac, def_type), src[0]);
+ if (ctx->abi->clamp_div_by_zero)
+ result = ac_build_fmin(&ctx->ac, result,
+ LLVMConstReal(ac_to_float_type(&ctx->ac, def_type), FLT_MAX));
break;
case nir_op_frexp_exp:
src[0] = ac_to_float(&ctx->ac, src[0]);
@@ -900,7 +906,7 @@
case nir_op_ffma:
/* FMA is better on GFX10, because it has FMA units instead of MUL-ADD units. */
result = emit_intrin_3f_param(&ctx->ac, ctx->ac.chip_class >= GFX10 ? "llvm.fma" : "llvm.fmuladd",
- ac_to_float_type(&ctx->ac, def_type), src[0], src[1], src[2]);
+ ac_to_float_type(&ctx->ac, def_type), src[0], src[1], src[2]);
break;
case nir_op_ldexp:
src[0] = ac_to_float(&ctx->ac, src[0]);
diff --git a/src/amd/llvm/ac_shader_abi.h b/src/amd/llvm/ac_shader_abi.h
index aa31ff9..80b1554 100644
--- a/src/amd/llvm/ac_shader_abi.h
+++ b/src/amd/llvm/ac_shader_abi.h
@@ -192,6 +192,9 @@
/* Whether undef values must be converted to zero */
bool convert_undef_to_zero;
+
+ /* Clamp div by 0 (so it won't produce NaN) */
+ bool clamp_div_by_zero;
};
#endif /* AC_SHADER_ABI_H */
