All of lore.kernel.org
 help / color / mirror / Atom feed
From: Richard Henderson <richard.henderson@linaro.org>
To: qemu-devel@nongnu.org
Cc: qemu-arm@nongnu.org
Subject: [PATCH v5 80/81] target/arm: Implement integer matrix multiply accumulate
Date: Fri, 16 Apr 2021 14:18:53 -0700	[thread overview]
Message-ID: <20210416211853.1591708-1-richard.henderson@linaro.org> (raw)
In-Reply-To: <20210416210240.1591291-1-richard.henderson@linaro.org>

This is {S,U,US}MMLA for both AArch64 AdvSIMD and SVE,
and V{S,U,US}MMLA.S8 for AArch32 NEON.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/arm/helper.h             |  7 +++
 target/arm/neon-shared.decode   |  7 +++
 target/arm/sve.decode           |  6 +++
 target/arm/translate-a64.c      | 18 ++++++++
 target/arm/translate-sve.c      | 27 ++++++++++++
 target/arm/vec_helper.c         | 77 +++++++++++++++++++++++++++++++++
 target/arm/translate-neon.c.inc | 27 ++++++++++++
 7 files changed, 169 insertions(+)

diff --git a/target/arm/helper.h b/target/arm/helper.h
index e8b16a401f..33df62f44d 100644
--- a/target/arm/helper.h
+++ b/target/arm/helper.h
@@ -994,6 +994,13 @@ DEF_HELPER_FLAGS_6(sve2_fmlal_zzxw_s, TCG_CALL_NO_RWG,
 
 DEF_HELPER_FLAGS_4(gvec_xar_d, TCG_CALL_NO_RWG, void, ptr, ptr, ptr, i32)
 
+DEF_HELPER_FLAGS_5(gvec_smmla_b, TCG_CALL_NO_RWG,
+                   void, ptr, ptr, ptr, ptr, i32)
+DEF_HELPER_FLAGS_5(gvec_ummla_b, TCG_CALL_NO_RWG,
+                   void, ptr, ptr, ptr, ptr, i32)
+DEF_HELPER_FLAGS_5(gvec_usmmla_b, TCG_CALL_NO_RWG,
+                   void, ptr, ptr, ptr, ptr, i32)
+
 #ifdef TARGET_AARCH64
 #include "helper-a64.h"
 #include "helper-sve.h"
diff --git a/target/arm/neon-shared.decode b/target/arm/neon-shared.decode
index 5befaec87b..cc9f4cdd85 100644
--- a/target/arm/neon-shared.decode
+++ b/target/arm/neon-shared.decode
@@ -59,6 +59,13 @@ VFML           1111 110 0 s:1 . 10 .... .... 1000 . 0 . 1 .... \
 VFML           1111 110 0 s:1 . 10 .... .... 1000 . 1 . 1 .... \
                vm=%vm_dp vn=%vn_dp vd=%vd_dp q=1
 
+VSMMLA         1111 1100 0.10 .... .... 1100 .1.0 .... \
+               vm=%vm_dp vn=%vn_dp vd=%vd_dp
+VUMMLA         1111 1100 0.10 .... .... 1100 .1.1 .... \
+               vm=%vm_dp vn=%vn_dp vd=%vd_dp
+VUSMMLA        1111 1100 1.10 .... .... 1100 .1.0 .... \
+               vm=%vm_dp vn=%vn_dp vd=%vd_dp
+
 VCMLA_scalar   1111 1110 0 . rot:2 .... .... 1000 . q:1 index:1 0 vm:4 \
                vn=%vn_dp vd=%vd_dp size=1
 VCMLA_scalar   1111 1110 1 . rot:2 .... .... 1000 . q:1 . 0 .... \
diff --git a/target/arm/sve.decode b/target/arm/sve.decode
index 63870b7539..3d7c4fa6e5 100644
--- a/target/arm/sve.decode
+++ b/target/arm/sve.decode
@@ -1364,6 +1364,12 @@ USHLLT          01000101 .. 0 ..... 1010 11 ..... .....  @rd_rn_tszimm_shl
 EORBT           01000101 .. 0 ..... 10010 0 ..... .....  @rd_rn_rm
 EORTB           01000101 .. 0 ..... 10010 1 ..... .....  @rd_rn_rm
 
+## SVE integer matrix multiply accumulate
+
+SMMLA           01000101 00 0 ..... 10011 0 ..... .....  @rda_rn_rm_e0
+USMMLA          01000101 10 0 ..... 10011 0 ..... .....  @rda_rn_rm_e0
+UMMLA           01000101 11 0 ..... 10011 0 ..... .....  @rda_rn_rm_e0
+
 ## SVE2 bitwise permute
 
 BEXT            01000101 .. 0 ..... 1011 00 ..... .....  @rd_rn_rm
diff --git a/target/arm/translate-a64.c b/target/arm/translate-a64.c
index 0d45a44f51..668edf3a00 100644
--- a/target/arm/translate-a64.c
+++ b/target/arm/translate-a64.c
@@ -12197,6 +12197,15 @@ static void disas_simd_three_reg_same_extra(DisasContext *s, uint32_t insn)
         }
         feature = dc_isar_feature(aa64_i8mm, s);
         break;
+    case 0x04: /* SMMLA */
+    case 0x14: /* UMMLA */
+    case 0x05: /* USMMLA */
+        if (!is_q || size != MO_32) {
+            unallocated_encoding(s);
+            return;
+        }
+        feature = dc_isar_feature(aa64_i8mm, s);
+        break;
     case 0x18: /* FCMLA, #0 */
     case 0x19: /* FCMLA, #90 */
     case 0x1a: /* FCMLA, #180 */
@@ -12241,6 +12250,15 @@ static void disas_simd_three_reg_same_extra(DisasContext *s, uint32_t insn)
         gen_gvec_op4_ool(s, is_q, rd, rn, rm, rd, 0, gen_helper_gvec_usdot_b);
         return;
 
+    case 0x04: /* SMMLA, UMMLA */
+        gen_gvec_op4_ool(s, 1, rd, rn, rm, rd, 0,
+                         u ? gen_helper_gvec_ummla_b
+                         : gen_helper_gvec_smmla_b);
+        return;
+    case 0x05: /* USMMLA */
+        gen_gvec_op4_ool(s, 1, rd, rn, rm, rd, 0, gen_helper_gvec_usmmla_b);
+        return;
+
     case 0x8: /* FCMLA, #0 */
     case 0x9: /* FCMLA, #90 */
     case 0xa: /* FCMLA, #180 */
diff --git a/target/arm/translate-sve.c b/target/arm/translate-sve.c
index ae628968da..cb0e7a1f68 100644
--- a/target/arm/translate-sve.c
+++ b/target/arm/translate-sve.c
@@ -8543,3 +8543,30 @@ static bool trans_FMLSLT_zzxw(DisasContext *s, arg_rrxr_esz *a)
 {
     return do_FMLAL_zzxw(s, a, true, true);
 }
+
+static bool do_i8mm_zzzz_ool(DisasContext *s, arg_rrrr_esz *a,
+                             gen_helper_gvec_4 *fn, int data)
+{
+    if (!dc_isar_feature(aa64_sve_i8mm, s)) {
+        return false;
+    }
+    if (sve_access_check(s)) {
+        gen_gvec_ool_zzzz(s, fn, a->rd, a->rn, a->rm, a->ra, data);
+    }
+    return true;
+}
+
+static bool trans_SMMLA(DisasContext *s, arg_rrrr_esz *a)
+{
+    return do_i8mm_zzzz_ool(s, a, gen_helper_gvec_smmla_b, 0);
+}
+
+static bool trans_USMMLA(DisasContext *s, arg_rrrr_esz *a)
+{
+    return do_i8mm_zzzz_ool(s, a, gen_helper_gvec_usmmla_b, 0);
+}
+
+static bool trans_UMMLA(DisasContext *s, arg_rrrr_esz *a)
+{
+    return do_i8mm_zzzz_ool(s, a, gen_helper_gvec_ummla_b, 0);
+}
diff --git a/target/arm/vec_helper.c b/target/arm/vec_helper.c
index ea08b15c55..6c9f1e5146 100644
--- a/target/arm/vec_helper.c
+++ b/target/arm/vec_helper.c
@@ -2578,3 +2578,80 @@ void HELPER(gvec_xar_d)(void *vd, void *vn, void *vm, uint32_t desc)
     }
     clear_tail(d, opr_sz * 8, simd_maxsz(desc));
 }
+
+/*
+ * Integer matrix-multiply accumulate
+ */
+
+static uint32_t do_smmla_b(uint32_t sum, void *vn, void *vm)
+{
+    int8_t *n = vn, *m = vm;
+
+    for (intptr_t k = 0; k < 8; ++k) {
+        sum += n[H1(k)] * m[H1(k)];
+    }
+    return sum;
+}
+
+static uint32_t do_ummla_b(uint32_t sum, void *vn, void *vm)
+{
+    uint8_t *n = vn, *m = vm;
+
+    for (intptr_t k = 0; k < 8; ++k) {
+        sum += n[H1(k)] * m[H1(k)];
+    }
+    return sum;
+}
+
+static uint32_t do_usmmla_b(uint32_t sum, void *vn, void *vm)
+{
+    uint8_t *n = vn;
+    int8_t *m = vm;
+
+    for (intptr_t k = 0; k < 8; ++k) {
+        sum += n[H1(k)] * m[H1(k)];
+    }
+    return sum;
+}
+
+static void do_mmla_b(void *vd, void *vn, void *vm, void *va, uint32_t desc,
+                      uint32_t (*inner_loop)(uint32_t, void *, void *))
+{
+    intptr_t seg, opr_sz = simd_oprsz(desc);
+
+    for (seg = 0; seg < opr_sz; seg += 16) {
+        uint32_t *d = vd + seg;
+        uint32_t *a = va + seg;
+        uint32_t sum0, sum1, sum2, sum3;
+
+        /*
+         * Process the entire segment at once, writing back the
+         * results only after we've consumed all of the inputs.
+         *
+         * Key to indicies by column:
+         *          i   j                  i             j
+         */
+        sum0 = a[H4(0 + 0)];
+        sum0 = inner_loop(sum0, vn + seg + 0, vm + seg + 0);
+        sum1 = a[H4(0 + 1)];
+        sum1 = inner_loop(sum1, vn + seg + 0, vm + seg + 8);
+        sum2 = a[H4(2 + 0)];
+        sum2 = inner_loop(sum2, vn + seg + 8, vm + seg + 0);
+        sum3 = a[H4(2 + 1)];
+        sum3 = inner_loop(sum3, vn + seg + 8, vm + seg + 8);
+
+        d[H4(0)] = sum0;
+        d[H4(1)] = sum1;
+        d[H4(2)] = sum2;
+        d[H4(3)] = sum3;
+    }
+    clear_tail(vd, opr_sz, simd_maxsz(desc));
+}
+
+#define DO_MMLA_B(NAME, INNER) \
+    void HELPER(NAME)(void *vd, void *vn, void *vm, void *va, uint32_t desc) \
+    { do_mmla_b(vd, vn, vm, va, desc, INNER); }
+
+DO_MMLA_B(gvec_smmla_b, do_smmla_b)
+DO_MMLA_B(gvec_ummla_b, do_ummla_b)
+DO_MMLA_B(gvec_usmmla_b, do_usmmla_b)
diff --git a/target/arm/translate-neon.c.inc b/target/arm/translate-neon.c.inc
index c322615915..f1893b1dc8 100644
--- a/target/arm/translate-neon.c.inc
+++ b/target/arm/translate-neon.c.inc
@@ -4027,3 +4027,30 @@ static bool trans_VTRN(DisasContext *s, arg_2misc *a)
     tcg_temp_free_i32(tmp2);
     return true;
 }
+
+static bool trans_VSMMLA(DisasContext *s, arg_VSMMLA *a)
+{
+    if (!dc_isar_feature(aa32_i8mm, s)) {
+        return false;
+    }
+    return do_neon_ddda(s, 7, a->vd, a->vn, a->vm, 0,
+                        gen_helper_gvec_smmla_b);
+}
+
+static bool trans_VUMMLA(DisasContext *s, arg_VUMMLA *a)
+{
+    if (!dc_isar_feature(aa32_i8mm, s)) {
+        return false;
+    }
+    return do_neon_ddda(s, 7, a->vd, a->vn, a->vm, 0,
+                        gen_helper_gvec_ummla_b);
+}
+
+static bool trans_VUSMMLA(DisasContext *s, arg_VUSMMLA *a)
+{
+    if (!dc_isar_feature(aa32_i8mm, s)) {
+        return false;
+    }
+    return do_neon_ddda(s, 7, a->vd, a->vn, a->vm, 0,
+                        gen_helper_gvec_usmmla_b);
+}
-- 
2.25.1



  parent reply	other threads:[~2021-04-16 22:07 UTC|newest]

Thread overview: 84+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-16 21:01 [PATCH v5 for-6.1 00/81] target/arm: Implement SVE2 Richard Henderson
2021-04-16 21:01 ` [PATCH v5 01/81] target/arm: Add ID_AA64ZFR0 fields and isar_feature_aa64_sve2 Richard Henderson
2021-04-16 21:01 ` [PATCH v5 02/81] target/arm: Implement SVE2 Integer Multiply - Unpredicated Richard Henderson
2021-04-16 21:01 ` [PATCH v5 03/81] target/arm: Implement SVE2 integer pairwise add and accumulate long Richard Henderson
2021-04-16 21:01 ` [PATCH v5 04/81] target/arm: Implement SVE2 integer unary operations (predicated) Richard Henderson
2021-04-16 21:01 ` [PATCH v5 05/81] target/arm: Split out saturating/rounding shifts from neon Richard Henderson
2021-04-16 21:01 ` [PATCH v5 06/81] target/arm: Implement SVE2 saturating/rounding bitwise shift left (predicated) Richard Henderson
2021-04-16 21:01 ` [PATCH v5 07/81] target/arm: Implement SVE2 integer halving add/subtract (predicated) Richard Henderson
2021-04-16 21:01 ` [PATCH v5 08/81] target/arm: Implement SVE2 integer pairwise arithmetic Richard Henderson
2021-04-16 21:01 ` [PATCH v5 09/81] target/arm: Implement SVE2 saturating add/subtract (predicated) Richard Henderson
2021-04-16 21:01 ` [PATCH v5 10/81] target/arm: Implement SVE2 integer add/subtract long Richard Henderson
2021-04-16 21:01 ` [PATCH v5 11/81] target/arm: Implement SVE2 integer add/subtract interleaved long Richard Henderson
2021-04-16 21:01 ` [PATCH v5 12/81] target/arm: Implement SVE2 integer add/subtract wide Richard Henderson
2021-04-16 21:01 ` [PATCH v5 13/81] target/arm: Implement SVE2 integer multiply long Richard Henderson
2021-04-16 21:01 ` [PATCH v5 14/81] target/arm: Implement PMULLB and PMULLT Richard Henderson
2021-04-16 21:01 ` [PATCH v5 15/81] target/arm: Implement SVE2 bitwise shift left long Richard Henderson
2021-04-16 21:01 ` [PATCH v5 16/81] target/arm: Implement SVE2 bitwise exclusive-or interleaved Richard Henderson
2021-04-16 21:01 ` [PATCH v5 17/81] target/arm: Implement SVE2 bitwise permute Richard Henderson
2021-04-16 21:01 ` [PATCH v5 18/81] target/arm: Implement SVE2 complex integer add Richard Henderson
2021-04-16 21:01 ` [PATCH v5 19/81] target/arm: Implement SVE2 integer absolute difference and accumulate long Richard Henderson
2021-04-16 21:01 ` [PATCH v5 20/81] target/arm: Implement SVE2 integer add/subtract long with carry Richard Henderson
2021-04-16 21:01 ` [PATCH v5 21/81] target/arm: Implement SVE2 bitwise shift right and accumulate Richard Henderson
2021-04-16 21:01 ` [PATCH v5 22/81] target/arm: Implement SVE2 bitwise shift and insert Richard Henderson
2021-04-16 21:01 ` [PATCH v5 23/81] target/arm: Implement SVE2 integer absolute difference and accumulate Richard Henderson
2021-04-16 21:01 ` [PATCH v5 24/81] target/arm: Implement SVE2 saturating extract narrow Richard Henderson
2021-04-16 21:01 ` [PATCH v5 25/81] target/arm: Implement SVE2 floating-point pairwise Richard Henderson
2021-04-16 21:01 ` [PATCH v5 26/81] target/arm: Implement SVE2 SHRN, RSHRN Richard Henderson
2021-04-16 21:01 ` [PATCH v5 27/81] target/arm: Implement SVE2 SQSHRUN, SQRSHRUN Richard Henderson
2021-04-16 21:01 ` [PATCH v5 28/81] target/arm: Implement SVE2 UQSHRN, UQRSHRN Richard Henderson
2021-04-16 21:01 ` [PATCH v5 29/81] target/arm: Implement SVE2 SQSHRN, SQRSHRN Richard Henderson
2021-04-16 21:01 ` [PATCH v5 30/81] target/arm: Implement SVE2 WHILEGT, WHILEGE, WHILEHI, WHILEHS Richard Henderson
2021-04-16 21:01 ` [PATCH v5 31/81] target/arm: Implement SVE2 WHILERW, WHILEWR Richard Henderson
2021-04-16 21:01 ` [PATCH v5 32/81] target/arm: Implement SVE2 bitwise ternary operations Richard Henderson
2021-04-16 21:01 ` [PATCH v5 33/81] target/arm: Implement SVE2 MATCH, NMATCH Richard Henderson
2021-04-16 21:01 ` [PATCH v5 34/81] target/arm: Implement SVE2 saturating multiply-add long Richard Henderson
2021-04-16 21:01 ` [PATCH v5 35/81] target/arm: Implement SVE2 saturating multiply-add high Richard Henderson
2021-04-16 21:01 ` [PATCH v5 36/81] target/arm: Implement SVE2 integer multiply-add long Richard Henderson
2021-04-16 21:01 ` [PATCH v5 37/81] target/arm: Implement SVE2 complex integer multiply-add Richard Henderson
2021-04-16 21:01 ` [PATCH v5 38/81] target/arm: Implement SVE2 ADDHNB, ADDHNT Richard Henderson
2021-04-16 21:01 ` [PATCH v5 39/81] target/arm: Implement SVE2 RADDHNB, RADDHNT Richard Henderson
2021-04-16 21:01 ` [PATCH v5 40/81] target/arm: Implement SVE2 SUBHNB, SUBHNT Richard Henderson
2021-04-16 21:02 ` [PATCH v5 41/81] target/arm: Implement SVE2 RSUBHNB, RSUBHNT Richard Henderson
2021-04-16 21:02 ` [PATCH v5 42/81] target/arm: Implement SVE2 HISTCNT, HISTSEG Richard Henderson
2021-04-16 21:02 ` [PATCH v5 43/81] target/arm: Implement SVE2 XAR Richard Henderson
2021-04-16 21:02 ` [PATCH v5 44/81] target/arm: Implement SVE2 scatter store insns Richard Henderson
2021-04-16 21:02 ` [PATCH v5 45/81] target/arm: Implement SVE2 gather load insns Richard Henderson
2021-04-16 21:02 ` [PATCH v5 46/81] target/arm: Implement SVE2 FMMLA Richard Henderson
2021-04-16 21:02 ` [PATCH v5 47/81] target/arm: Implement SVE2 SPLICE, EXT Richard Henderson
2021-04-16 21:02 ` [PATCH v5 48/81] target/arm: Pass separate addend to {U, S}DOT helpers Richard Henderson
2021-04-16 21:02 ` [PATCH v5 49/81] target/arm: Pass separate addend to FCMLA helpers Richard Henderson
2021-05-13 10:48   ` Peter Maydell
2021-04-16 21:02 ` [PATCH v5 50/81] target/arm: Split out formats for 2 vectors + 1 index Richard Henderson
2021-04-16 21:02 ` [PATCH v5 51/81] target/arm: Split out formats for 3 " Richard Henderson
2021-04-16 21:02 ` [PATCH v5 52/81] target/arm: Implement SVE2 integer multiply (indexed) Richard Henderson
2021-04-16 21:02 ` [PATCH v5 53/81] target/arm: Implement SVE2 integer multiply-add (indexed) Richard Henderson
2021-04-16 21:02 ` [PATCH v5 54/81] target/arm: Implement SVE2 saturating multiply-add high (indexed) Richard Henderson
2021-04-16 21:02 ` [PATCH v5 55/81] target/arm: Implement SVE2 saturating multiply-add (indexed) Richard Henderson
2021-04-16 21:02 ` [PATCH v5 56/81] target/arm: Implement SVE2 saturating multiply (indexed) Richard Henderson
2021-04-16 21:02 ` [PATCH v5 57/81] target/arm: Implement SVE2 signed saturating doubling multiply high Richard Henderson
2021-04-16 21:02 ` [PATCH v5 58/81] target/arm: Implement SVE2 saturating multiply high (indexed) Richard Henderson
2021-04-16 21:02 ` [PATCH v5 59/81] target/arm: Implement SVE mixed sign dot product (indexed) Richard Henderson
2021-04-16 21:02 ` [PATCH v5 60/81] target/arm: Implement SVE mixed sign dot product Richard Henderson
2021-04-16 21:02 ` [PATCH v5 61/81] target/arm: Implement SVE2 crypto unary operations Richard Henderson
2021-04-16 21:02 ` [PATCH v5 62/81] target/arm: Implement SVE2 crypto destructive binary operations Richard Henderson
2021-04-16 21:02 ` [PATCH v5 63/81] target/arm: Implement SVE2 crypto constructive " Richard Henderson
2021-04-16 21:02 ` [PATCH v5 64/81] target/arm: Implement SVE2 TBL, TBX Richard Henderson
2021-04-16 21:02 ` [PATCH v5 65/81] target/arm: Implement SVE2 FCVTNT Richard Henderson
2021-04-16 21:02 ` [PATCH v5 66/81] target/arm: Implement SVE2 FCVTLT Richard Henderson
2021-04-16 21:02 ` [PATCH v5 67/81] target/arm: Implement SVE2 FCVTXNT, FCVTX Richard Henderson
2021-04-16 21:02 ` [PATCH v5 68/81] target/arm: Implement SVE2 FLOGB Richard Henderson
2021-04-16 21:02 ` [PATCH v5 69/81] target/arm: Share table of sve load functions Richard Henderson
2021-04-16 21:02 ` [PATCH v5 70/81] target/arm: Implement SVE2 LD1RO Richard Henderson
2021-04-16 21:02 ` [PATCH v5 71/81] target/arm: Implement 128-bit ZIP, UZP, TRN Richard Henderson
2021-04-16 21:02 ` [PATCH v5 72/81] target/arm: Implement SVE2 bitwise shift immediate Richard Henderson
2021-04-16 21:02 ` [PATCH v5 73/81] target/arm: Implement SVE2 fp multiply-add long Richard Henderson
2021-04-16 21:02 ` [PATCH v5 74/81] target/arm: Implement aarch64 SUDOT, USDOT Richard Henderson
2021-04-16 21:02 ` [PATCH v5 75/81] target/arm: Split out do_neon_ddda_fpst Richard Henderson
2021-04-16 21:02 ` [PATCH v5 76/81] target/arm: Remove unused fpst from VDOT_scalar Richard Henderson
2021-04-16 21:02 ` [PATCH v5 77/81] target/arm: Fix decode for VDOT (indexed) Richard Henderson
2021-04-16 21:02 ` [PATCH v5 78/81] target/arm: Split decode of VSDOT and VUDOT Richard Henderson
2021-04-16 21:02 ` [PATCH v5 79/81] target/arm: Implement aarch32 VSUDOT, VUSDOT Richard Henderson
2021-04-16 21:18 ` Richard Henderson [this message]
2021-04-16 21:19 ` [PATCH v5 81/81] target/arm: Enable SVE2 and some extensions Richard Henderson
2021-04-16 22:46 ` [PATCH v5 for-6.1 00/81] target/arm: Implement SVE2 no-reply

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210416211853.1591708-1-richard.henderson@linaro.org \
    --to=richard.henderson@linaro.org \
    --cc=qemu-arm@nongnu.org \
    --cc=qemu-devel@nongnu.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.