From 1551f6be9d67cfa8ca4d33d2946c0bec205e39c7 Mon Sep 17 00:00:00 2001
From: Richard Henderson <richard.henderson@linaro.org>
Date: Mon, 1 Mar 2021 19:23:36 -0500
Subject: [PATCH] tcg: Adjust simd_desc size encoding

With larger vector sizes, it turns out oprsz == maxsz, and we only
need to represent mismatch for oprsz <= 32. We do, however, need
to represent larger oprsz and do so without reducing SIMD_DATA_BITS.

Reduce the size of the oprsz field and increase the maxsz field.
Steal the oprsz value of 24 to indicate equality with maxsz.

Backports e2e7168a214b0ed98dc357bba96816486a289762
---
 qemu/tcg/tcg-gvec-desc.h | 38 +++++++++++++++++++++++++-------------
 qemu/tcg/tcg-op-gvec.c   | 20 +++++++++++++++-----
 2 files changed, 40 insertions(+), 18 deletions(-)

diff --git a/qemu/tcg/tcg-gvec-desc.h b/qemu/tcg/tcg-gvec-desc.h
index 0224ac3e..704bd864 100644
--- a/qemu/tcg/tcg-gvec-desc.h
+++ b/qemu/tcg/tcg-gvec-desc.h
@@ -20,29 +20,41 @@
 #ifndef TCG_TCG_GVEC_DESC_H
 #define TCG_TCG_GVEC_DESC_H
 
-/* ??? These bit widths are set for ARM SVE, maxing out at 256 byte vectors. */
-#define SIMD_OPRSZ_SHIFT   0
-#define SIMD_OPRSZ_BITS    5
+/*
+ * This configuration allows MAXSZ to represent 2048 bytes, and
+ * OPRSZ to match MAXSZ, or represent the smaller values 8, 16, or 32.
+ *
+ * Encode this with:
+ *   0, 1, 3 -> 8, 16, 32
+ *   2       -> maxsz
+ *
+ * This steals the input that would otherwise map to 24 to match maxsz.
+ */
+#define SIMD_MAXSZ_SHIFT   0
+#define SIMD_MAXSZ_BITS    8
 
-#define SIMD_MAXSZ_SHIFT   (SIMD_OPRSZ_SHIFT + SIMD_OPRSZ_BITS)
-#define SIMD_MAXSZ_BITS    5
+#define SIMD_OPRSZ_SHIFT   (SIMD_MAXSZ_SHIFT + SIMD_MAXSZ_BITS)
+#define SIMD_OPRSZ_BITS    2
 
-#define SIMD_DATA_SHIFT    (SIMD_MAXSZ_SHIFT + SIMD_MAXSZ_BITS)
+#define SIMD_DATA_SHIFT    (SIMD_OPRSZ_SHIFT + SIMD_OPRSZ_BITS)
 #define SIMD_DATA_BITS     (32 - SIMD_DATA_SHIFT)
 
 /* Create a descriptor from components.  */
 uint32_t simd_desc(uint32_t oprsz, uint32_t maxsz, int32_t data);
 
-/* Extract the operation size from a descriptor.  */
-static inline intptr_t simd_oprsz(uint32_t desc)
-{
-    return (extract32(desc, SIMD_OPRSZ_SHIFT, SIMD_OPRSZ_BITS) + 1) * 8;
-}
-
 /* Extract the max vector size from a descriptor.  */
 static inline intptr_t simd_maxsz(uint32_t desc)
 {
-    return (extract32(desc, SIMD_MAXSZ_SHIFT, SIMD_MAXSZ_BITS) + 1) * 8;
+    return extract32(desc, SIMD_MAXSZ_SHIFT, SIMD_MAXSZ_BITS) * 8 + 8;
+}
+
+/* Extract the operation size from a descriptor.  */
+static inline intptr_t simd_oprsz(uint32_t desc)
+{
+    uint32_t f = extract32(desc, SIMD_OPRSZ_SHIFT, SIMD_OPRSZ_BITS);
+    intptr_t o = f * 8 + 8;
+    intptr_t m = simd_maxsz(desc);
+    return f == 2 ? m : o;
 }
 
 /* Extract the operation-specific data from a descriptor.  */
diff --git a/qemu/tcg/tcg-op-gvec.c b/qemu/tcg/tcg-op-gvec.c
index b27c47f9..e4cdfb9c 100644
--- a/qemu/tcg/tcg-op-gvec.c
+++ b/qemu/tcg/tcg-op-gvec.c
@@ -37,11 +37,21 @@ static const TCGOpcode vecop_list_empty[1] = { 0 };
    of the operand offsets so that we can check them all at once.  */
 static void check_size_align(uint32_t oprsz, uint32_t maxsz, uint32_t ofs)
 {
-    uint32_t opr_align = oprsz >= 16 ? 15 : 7;
-    uint32_t max_align = maxsz >= 16 || oprsz >= 16 ? 15 : 7;
-    tcg_debug_assert(oprsz > 0);
-    tcg_debug_assert(oprsz <= maxsz);
-    tcg_debug_assert((oprsz & opr_align) == 0);
+    uint32_t max_align;
+
+    switch (oprsz) {
+    case 8:
+    case 16:
+    case 32:
+        tcg_debug_assert(oprsz <= maxsz);
+        break;
+    default:
+        tcg_debug_assert(oprsz == maxsz);
+        break;
+    }
+    tcg_debug_assert(maxsz <= (8 << SIMD_MAXSZ_BITS));
+
+    max_align = maxsz >= 16 ? 15 : 7;
     tcg_debug_assert((maxsz & max_align) == 0);
     tcg_debug_assert((ofs & max_align) == 0);
 }