From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id 105FC3858412 for ; Mon, 24 Oct 2022 06:04:55 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 105FC3858412 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1666591494; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=5Bt6zPEOx1j/IPnV66DsAeeJFzQSVa6J3Ok6Zd1d7LM=; b=MZVbthAWM70Ex4rvjiA8Z0e/ceJMqqedyRwHuEzdyMKim/Rok1yZPXMLfPkWvAhIsACbuL nkEkYAJeEMpVXWQjXOcMIn+LLmRMka7zuTPZEkaZjU6mkFQDlP0c6D3cHS/+CFysJ0Dkx3 PewUoMcduIN/rASe7Ri1Le0Ssy1jvJo= Received: from mail-yw1-f199.google.com (mail-yw1-f199.google.com [209.85.128.199]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_128_GCM_SHA256) id us-mta-650-hjusWGNUN12-_kOE6aRi7A-1; Mon, 24 Oct 2022 02:04:52 -0400 X-MC-Unique: hjusWGNUN12-_kOE6aRi7A-1 Received: by mail-yw1-f199.google.com with SMTP id 00721157ae682-369d18a90c3so75197337b3.0 for ; Sun, 23 Oct 2022 23:04:52 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=5Bt6zPEOx1j/IPnV66DsAeeJFzQSVa6J3Ok6Zd1d7LM=; b=C9D+EVVofIQ1Sv3k1yycsXf8l/Kznul29BkoCjwy07o/K9wTCrFrVAL1diXQ+/kGx2 7rcw+oZ3idJezdHIjq2HmiTpOgHzhzDNzvPr4TbBpi31G5oBLlPdhK6wxRXHI/mYeIph KEdVQCh52bEN1edddVP/E6ecSg5jMeCGnzwTuY8mq7IQa66PcFanifss1L+Ga3m9UgGz s9ePgNMtLofcabvjFwiKyELcxU6/hNFtBU7Yy3xZBuN+RUs6lZB6ScpdXh7yJqKE+pjQ eYKFfN626gP9KANyeL0w+5yHwZeD+Qe0g9PsmEVnLiWs7P7y3ei0yUehq9NlnOe8lKfB ildQ== X-Gm-Message-State: ACrzQf2QewgW9tp9GycGXuB5K688IfcAsE4Mb8q0HpFtjb4WEl55wZo/ YUVfQDsVK8jtL0UQZBTUekvlQI0+DvaaI0lqJNYB6UdvrwdX8KruSNCg3nYZh9A5fZfPSCZ7w5Y d9O982I+bFRRay7TromuW1qnqd5J/lpOLkw== X-Received: by 2002:a25:6a57:0:b0:6af:c9f1:1f8d with SMTP id f84-20020a256a57000000b006afc9f11f8dmr27145626ybc.3.1666591492195; Sun, 23 Oct 2022 23:04:52 -0700 (PDT) X-Google-Smtp-Source: AMsMyM5sz526ggYeRaX02lMzsoSRcTJBkmGI8fH7bKATDteuJ2NNltZ1UMI8W3x/ljsoQQ1JCFaauh3gsRtlRf5jX1E= X-Received: by 2002:a25:6a57:0:b0:6af:c9f1:1f8d with SMTP id f84-20020a256a57000000b006afc9f11f8dmr27145606ybc.3.1666591491893; Sun, 23 Oct 2022 23:04:51 -0700 (PDT) MIME-Version: 1.0 References: <20221013123649.474497-1-aldyh@redhat.com> In-Reply-To: From: Aldy Hernandez Date: Mon, 24 Oct 2022 08:04:40 +0200 Message-ID: Subject: Re: [PATCH] [PR24021] Implement PLUS_EXPR range-op entry for floats. To: Jakub Jelinek Cc: GCC patches , Andrew MacLeod X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-5.8 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: PING On Mon, Oct 17, 2022 at 8:21 AM Aldy Hernandez wrote: > > On Thu, Oct 13, 2022 at 7:57 PM Jakub Jelinek wrote: > > > > On Thu, Oct 13, 2022 at 02:36:49PM +0200, Aldy Hernandez wrote: > > > +// Like real_arithmetic, but round the result to INF if the operation > > > +// produced inexact results. > > > +// > > > +// ?? There is still one problematic case, i387. With > > > +// -fexcess-precision=standard we perform most SF/DFmode arithmetic in > > > +// XFmode (long_double_type_node), so that case is OK. But without > > > +// -mfpmath=sse, all the SF/DFmode computations are in XFmode > > > +// precision (64-bit mantissa) and only occassionally rounded to > > > +// SF/DFmode (when storing into memory from the 387 stack). Maybe > > > +// this is ok as well though it is just occassionally more precise. ?? > > > + > > > +static void > > > +frange_arithmetic (enum tree_code code, tree type, > > > + REAL_VALUE_TYPE &result, > > > + const REAL_VALUE_TYPE &op1, > > > + const REAL_VALUE_TYPE &op2, > > > + const REAL_VALUE_TYPE &inf) > > > +{ > > > + REAL_VALUE_TYPE value; > > > + enum machine_mode mode = TYPE_MODE (type); > > > + bool mode_composite = MODE_COMPOSITE_P (mode); > > > + > > > + bool inexact = real_arithmetic (&value, code, &op1, &op2); > > > + real_convert (&result, mode, &value); > > > + > > > + // If real_convert above has rounded an inexact value to towards > > > + // inf, we can keep the result as is, otherwise we'll adjust by 1 ulp > > > + // later (real_nextafter). > > > + bool rounding = (flag_rounding_math > > > + && (real_isneg (&inf) > > > + ? real_less (&result, &value) > > > + : !real_less (&value, &result))); > > > > I thought the agreement during Cauldron was that we'd do this always, > > regardless of flag_rounding_math. > > Because excess precision (the fast one like on ia32 or -mfpmath=387 on > > x86_64), or -frounding-math, or FMA contraction can all increase precision > > and worst case it all behaves like -frounding-math for the ranges. > > > > So, perhaps use: > > if ((mode_composite || (real_isneg (&inf) ? real_less (&result, &value) > > : !real_less (&value, &result)) > > && (inexact || !real_identical (&result, &value)))) > > Done. > > > ? > > No need to do the real_isneg/real_less stuff for mode_composite, then > > we do it always for inexacts, but otherwise we check if the rounding > > performed by real.cc has been in the conservative direction (for upper > > bound to +inf, for lower bound to -inf), if yes, we don't need to do > > anything, if yes, we frange_nextafter. > > > > As discussed, for mode_composite, I think we want to do the extra > > stuff for inexact denormals and otherwise do the nextafter unconditionally, > > because our internal mode_composite representation isn't precise enough. > > > > > + // Be extra careful if there may be discrepancies between the > > > + // compile and runtime results. > > > + if ((rounding || mode_composite) > > > + && (inexact || !real_identical (&result, &value))) > > > + { > > > + if (mode_composite) > > > + { > > > + bool denormal = (result.sig[SIGSZ-1] & SIG_MSB) == 0; > > > > Use real_isdenormal here? > > Done. > > > Though, real_iszero needs the same thing. > > So... real_isdenormal() || real_iszero() as in the attached patch? > > > > > > + if (denormal) > > > + { > > > + REAL_VALUE_TYPE tmp; > > > > And explain here why is this, that IBM extended denormals have just > > DFmode precision. > > Done. > > > Though, now that I think about it, while this is correct for denormals, > > > > > + real_convert (&tmp, DFmode, &value); > > > + frange_nextafter (DFmode, tmp, inf); > > > + real_convert (&result, mode, &tmp); > > > + } > > > > there are also the cases where the higher double exponent is in the > > [__DBL_MIN_EXP__, __LDBL_MIN_EXP__] aka [-1021, -968] or so. > > https://en.wikipedia.org/wiki/Double-precision_floating-point_format > > If the upper double is denormal in the DFmode sense, so smaller absolute > > value than __DBL_MIN__, then doing nextafter in DFmode is the right thing to > > do, the lower double must be always +/- zero. > > Now, if the result is __DBL_MIN__, the upper double is already normalized > > but we can add __DBL_DENORM_MIN__ to it, which will make the number have > > 54-bit precision. > > If the result is __DBL_MIN__ * 2, we can again add __DBL_DENORM_MIN__ > > and make it 55-bit precision. Etc. until we reach __DBL_MIN__ * 2e53 > > where it acts like fully normalized 106-bit precision number. > > I must say I'm not really sure what real_nextafter is doing in those cases, > > I'm afraid it doesn't handle it correctly but the only other use > > of real_nextafter is guarded with: > > /* Don't handle composite modes, nor decimal, nor modes without > > inf or denorm at least for now. */ > > if (format->pnan < format->p > > || format->b == 10 > > || !format->has_inf > > || !format->has_denorm) > > return false; > > Dunno. Is there a conservative thing we can do for mode_composites > that aren't denormal or zero? > > How does this look? > Aldy