pan/va: Add constant lowering pass

Valhall has a lookup table for common constants. Add a pass to take
advantage of it, lowering away immediate indices.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15223>

src/panfrost/bifrost/meson.build

@@ -45,6 +45,7 @@ libpanfrost_bifrost_files = files(
   'bi_validate.c',
   'bir.c',
   'bifrost_compile.c',
+  'valhall/va_lower_constants.c',
   'valhall/va_optimize.c',
   'valhall/va_pack.c',
   'valhall/va_validate.c',

src/panfrost/bifrost/valhall/va_compiler.h

@@ -38,6 +38,7 @@ bool va_validate_fau(bi_instr *I);
 void va_validate(FILE *fp, bi_context *ctx);
 void va_repair_fau(bi_builder *b, bi_instr *I);
 void va_fuse_add_imm(bi_instr *I);
+void va_lower_constants(bi_context *ctx, bi_instr *I);
 uint64_t va_pack_instr(const bi_instr *I, unsigned flow);
 
 static inline unsigned
@@ -79,6 +80,15 @@ va_select_fau_page(const bi_instr *I)
    return 0;
 }
 
+/** Cycle model for Valhall. Results need to be normalized */
+struct va_stats {
+   /** Counts per pipe */
+   unsigned fma, cvt, sfu, v, ls, t;
+};
+
+void
+va_count_instr_stats(bi_instr *I, struct va_stats *stats);
+
 #ifdef __cplusplus
 } /* extern C */
 #endif

src/panfrost/bifrost/valhall/va_lower_constants.c

@@ -0,0 +1,179 @@
+/*
+ * Copyright (C) 2021 Collabora Ltd.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include "va_compiler.h"
+#include "valhall.h"
+#include "bi_builder.h"
+
+/* Only some special immediates are available, as specified in the Table of
+ * Immediates in the specification. Other immediates must be lowered, either to
+ * uniforms or to moves.
+ */
+
+static bi_index
+va_mov_imm(bi_builder *b, uint32_t imm)
+{
+   bi_index zero = bi_fau(BIR_FAU_IMMEDIATE | 0, false);
+   return bi_iadd_imm_i32(b, zero, imm);
+}
+
+static bi_index
+va_lut_index_32(uint32_t imm)
+{
+   for (unsigned i = 0; i < ARRAY_SIZE(valhall_immediates); ++i) {
+      if (valhall_immediates[i] == imm)
+         return va_lut(i);
+   }
+
+   return bi_null();
+}
+
+static bi_index
+va_lut_index_16(uint16_t imm)
+{
+   uint16_t *arr16 = (uint16_t *) valhall_immediates;
+
+   for (unsigned i = 0; i < (2 * ARRAY_SIZE(valhall_immediates)); ++i) {
+      if (arr16[i] == imm)
+         return bi_half(va_lut(i >> 1), i & 1);
+   }
+
+   return bi_null();
+}
+
+UNUSED static bi_index
+va_lut_index_8(uint8_t imm)
+{
+   uint8_t *arr8 = (uint8_t *) valhall_immediates;
+
+   for (unsigned i = 0; i < (4 * ARRAY_SIZE(valhall_immediates)); ++i) {
+      if (arr8[i] == imm)
+         return bi_byte(va_lut(i >> 2), i & 3);
+   }
+
+   return bi_null();
+}
+
+static bi_index
+va_demote_constant_fp16(uint32_t value)
+{
+   uint16_t fp16 = _mesa_float_to_half(uif(value));
+
+   /* Only convert if it is exact */
+   if (fui(_mesa_half_to_float(fp16)) == value)
+      return va_lut_index_16(fp16);
+   else
+      return bi_null();
+}
+
+static bi_index
+va_resolve_constant(bi_builder *b, uint32_t value, struct va_src_info info, bool staging)
+{
+   /* Try the constant as-is */
+   if (!staging) {
+      bi_index lut = va_lut_index_32(value);
+      if (!bi_is_null(lut)) return lut;
+   }
+
+   /* Try using a single half of a FP16 constant */
+   bool replicated_halves = (value & 0xFFFF) == (value >> 16);
+   if (!staging && info.swizzle && info.size == VA_SIZE_16 && replicated_halves) {
+      bi_index lut = va_lut_index_16(value & 0xFFFF);
+      if (!bi_is_null(lut)) return lut;
+   }
+
+   /* TODO: Distinguish sign extend from zero extend */
+#if 0
+   /* Try zero-extending a single byte */
+   if (!staging && info.widen && value <= UINT8_MAX) {
+      bi_index lut = va_lut_index_8(value);
+      if (!bi_is_null(lut)) return lut;
+   }
+
+   /* Try zero-extending a single halfword */
+   if (!staging && info.widen && value <= UINT16_MAX) {
+      bi_index lut = va_lut_index_16(value);
+      if (!bi_is_null(lut)) return lut;
+   }
+#endif
+
+   /* Try demoting the constant to FP16 */
+   if (!staging && info.swizzle && info.size == VA_SIZE_32) {
+      bi_index lut = va_demote_constant_fp16(value);
+      if (!bi_is_null(lut)) return lut;
+   }
+
+   /* TODO: Optimize to uniform */
+   return va_mov_imm(b, value);
+}
+
+void
+va_lower_constants(bi_context *ctx, bi_instr *I)
+{
+   bi_builder b = bi_init_builder(ctx, bi_before_instr(I));
+
+   bi_foreach_src(I, s) {
+      if (I->src[s].type == BI_INDEX_CONSTANT) {
+         /* abs(#c) is pointless, but -#c occurs in transcendental sequences */
+         assert(!I->src[s].abs && "redundant .abs modifier");
+
+         bool staging = (s < valhall_opcodes[I->op].nr_staging_srcs);
+         struct va_src_info info = va_src_info(I->op, s);
+         uint32_t value = I->src[s].value;
+         enum bi_swizzle swz = I->src[s].swizzle;
+
+         /* Resolve any swizzle, keeping in mind the different interpretations
+          * swizzles in different contexts.
+          */
+         if (info.size == VA_SIZE_32) {
+            /* Extracting a half from the 32-bit value */
+            if (swz == BI_SWIZZLE_H00)
+               value = (value & 0xFFFF);
+            else if (swz == BI_SWIZZLE_H11)
+               value = (value >> 16);
+            else
+               assert(swz == BI_SWIZZLE_H01);
+
+            /* FP16 -> FP32 */
+            if (info.swizzle && swz != BI_SWIZZLE_H01)
+               value = fui(_mesa_half_to_float(value));
+         } else if (info.size == VA_SIZE_16) {
+            assert(swz >= BI_SWIZZLE_H00 && swz <= BI_SWIZZLE_H11);
+            value = bi_apply_swizzle(value, swz);
+         } else if (info.size == VA_SIZE_8 && info.lanes) {
+            /* 8-bit extract */
+            unsigned chan = (swz - BI_SWIZZLE_B0000);
+            assert(chan < 4);
+
+            value = (value >> (8 * chan)) & 0xFF;
+         } else {
+            /* TODO: Any other special handling? */
+            value = bi_apply_swizzle(value, swz);
+         }
+
+         bi_index cons = va_resolve_constant(&b, value, info, staging);
+         cons.neg ^= I->src[s].neg;
+         I->src[s] = cons;
+      }
+   }
+}