From f02f71f38fc3c4a836c0b431ae5f705c7729bdf1 Mon Sep 17 00:00:00 2001
From: Richard Henderson <richard.henderson@linaro.org>
Date: Thu, 7 May 2020 10:19:23 -0400
Subject: [PATCH] tcg: Improve vector tail clearing

Better handling of non-power-of-2 tails as seen with Arm 8-byte
vector operations.

Backports commit f47db80cc073c0a7a22136c8296b5eca20c0e199 from qemu
---
 qemu/tcg/tcg-op-gvec.c | 82 ++++++++++++++++++++++++++++++++----------
 1 file changed, 63 insertions(+), 19 deletions(-)

diff --git a/qemu/tcg/tcg-op-gvec.c b/qemu/tcg/tcg-op-gvec.c
index 15c01eed..6e1171b6 100644
--- a/qemu/tcg/tcg-op-gvec.c
+++ b/qemu/tcg/tcg-op-gvec.c
@@ -327,11 +327,34 @@ void tcg_gen_gvec_5_ptr(TCGContext *s, uint32_t dofs, uint32_t aofs, uint32_t bo
    in units of LNSZ.  This limits the expansion of inline code.  */
 static inline bool check_size_impl(uint32_t oprsz, uint32_t lnsz)
 {
-    if (oprsz % lnsz == 0) {
-        uint32_t lnct = oprsz / lnsz;
-        return lnct >= 1 && lnct <= MAX_UNROLL;
+    uint32_t q, r;
+
+    if (oprsz < lnsz) {
+        return false;
     }
-    return false;
+
+    q = oprsz / lnsz;
+    r = oprsz % lnsz;
+    tcg_debug_assert((r & 7) == 0);
+
+    if (lnsz < 16) {
+        /* For sizes below 16, accept no remainder. */
+        if (r != 0) {
+            return false;
+        }
+    } else {
+        /*
+         * Recall that ARM SVE allows vector sizes that are not a
+         * power of 2, but always a multiple of 16.  The intent is
+         * that e.g. size == 80 would be expanded with 2x32 + 1x16.
+         * In addition, expand_clr needs to handle a multiple of 8.
+         * Thus we can handle the tail with one more operation per
+         * diminishing power of 2.
+         */
+        q += ctpop32(r);
+    }
+
+    return q <= MAX_UNROLL;
 }
 
 static void expand_clr(TCGContext *s, uint32_t dofs, uint32_t maxsz);
@@ -403,22 +426,31 @@ static void gen_dup_i64(TCGContext *s, unsigned vece, TCGv_i64 out, TCGv_i64 in)
 static TCGType choose_vector_type(const TCGOpcode *list, unsigned vece,
                                   uint32_t size, bool prefer_i64)
 {
-    if (TCG_TARGET_HAS_v256 && check_size_impl(size, 32)) {
-        /*
-         * Recall that ARM SVE allows vector sizes that are not a
-         * power of 2, but always a multiple of 16.  The intent is
-         * that e.g. size == 80 would be expanded with 2x32 + 1x16.
-         * It is hard to imagine a case in which v256 is supported
-         * but v128 is not, but check anyway.
-         */
-        if (tcg_can_emit_vecop_list(list, TCG_TYPE_V256, vece)
-            && (size % 32 == 0
-                || tcg_can_emit_vecop_list(list, TCG_TYPE_V128, vece))) {
-            return TCG_TYPE_V256;
-        }
+    /*
+     * Recall that ARM SVE allows vector sizes that are not a
+     * power of 2, but always a multiple of 16.  The intent is
+     * that e.g. size == 80 would be expanded with 2x32 + 1x16.
+     * It is hard to imagine a case in which v256 is supported
+     * but v128 is not, but check anyway.
+     * In addition, expand_clr needs to handle a multiple of 8.
+     */
+    if (TCG_TARGET_HAS_v256 &&
+        check_size_impl(size, 32) &&
+        tcg_can_emit_vecop_list(list, TCG_TYPE_V256, vece) &&
+        (!(size & 16) ||
+         (TCG_TARGET_HAS_v128 &&
+          tcg_can_emit_vecop_list(list, TCG_TYPE_V128, vece))) &&
+        (!(size & 8) ||
+         (TCG_TARGET_HAS_v64 &&
+          tcg_can_emit_vecop_list(list, TCG_TYPE_V64, vece)))) {
+        return TCG_TYPE_V256;
     }
-    if (TCG_TARGET_HAS_v128 && check_size_impl(size, 16)
-        && tcg_can_emit_vecop_list(list, TCG_TYPE_V128, vece)) {
+    if (TCG_TARGET_HAS_v128 &&
+        check_size_impl(size, 16) &&
+        tcg_can_emit_vecop_list(list, TCG_TYPE_V128, vece) &&
+        (!(size & 8) ||
+         (TCG_TARGET_HAS_v64 &&
+          tcg_can_emit_vecop_list(list, TCG_TYPE_V64, vece)))) {
         return TCG_TYPE_V128;
     }
     if (TCG_TARGET_HAS_v64 && !prefer_i64 && check_size_impl(size, 8)
@@ -433,6 +465,18 @@ static void do_dup_store(TCGContext *s, TCGType type, uint32_t dofs, uint32_t op
 {
     uint32_t i = 0;
 
+    tcg_debug_assert(oprsz >= 8);
+
+    /*
+     * This may be expand_clr for the tail of an operation, e.g.
+     * oprsz == 8 && maxsz == 64.  The first 8 bytes of this store
+     * are misaligned wrt the maximum vector size, so do that first.
+     */
+    if (dofs & 8) {
+        tcg_gen_stl_vec(s, t_vec, s->cpu_env, dofs + i, TCG_TYPE_V64);
+        i += 8;
+    }
+
     switch (type) {
     case TCG_TYPE_V256:
         /*