Reduce code size on x86 (32-bit and 64-bit).

The variables in structures in xz_dec_lzma2.c were reordered
so that the variables that the code references most are near
the beginning of the structure within 128 bytes. This allows
three bytes smaller instructions to access the variables, and
saves around 700-900 bytes in code size.

1 files changed, 65 insertions, 59 deletions

diff --git a/linux/lib/xz/xz_dec_lzma2.c b/linux/lib/xz/xz_dec_lzma2.c
index 0b8ddb6..ad36e29 100644
--- a/linux/lib/xz/xz_dec_lzma2.c
+++ b/linux/lib/xz/xz_dec_lzma2.c
@@ -130,31 +130,31 @@ struct lzma_len_dec {
 };
 
 struct lzma_dec {
-	/*
-	 * LZMA properties or related bit masks (number of literal
-	 * context bits, a mask dervied from the number of literal
-	 * position bits, and a mask dervied from the number
-	 * position bits)
-	 */
-	uint32_t lc;
-	uint32_t literal_pos_mask; /* (1 << lp) - 1 */
-	uint32_t pos_mask;         /* (1 << pb) - 1 */
-
-	/* Types of the most recently seen LZMA symbols */
-	enum lzma_state state;
-
 	/* Distances of latest four matches */
 	uint32_t rep0;
 	uint32_t rep1;
 	uint32_t rep2;
 	uint32_t rep3;
 
+	/* Types of the most recently seen LZMA symbols */
+	enum lzma_state state;
+
 	/*
 	 * Length of a match. This is updated so that dict_repeat can
 	 * be called again to finish repeating the whole match.
 	 */
 	uint32_t len;
 
+	/*
+	 * LZMA properties or related bit masks (number of literal
+	 * context bits, a mask dervied from the number of literal
+	 * position bits, and a mask dervied from the number
+	 * position bits)
+	 */
+	uint32_t lc;
+	uint32_t literal_pos_mask; /* (1 << lp) - 1 */
+	uint32_t pos_mask;         /* (1 << pb) - 1 */
+
 	/* If 1, it's a match. Otherwise it's a single 8-bit literal. */
 	uint16_t is_match[STATES][POS_STATES_MAX];
 
@@ -211,49 +211,59 @@ struct lzma_dec {
 	uint16_t literal[LITERAL_CODERS_MAX][LITERAL_CODER_SIZE];
 };
 
+struct lzma2_dec {
+	/* Position in xz_dec_lzma2_run(). */
+	enum lzma2_seq {
+		SEQ_CONTROL,
+		SEQ_UNCOMPRESSED_1,
+		SEQ_UNCOMPRESSED_2,
+		SEQ_COMPRESSED_0,
+		SEQ_COMPRESSED_1,
+		SEQ_PROPERTIES,
+		SEQ_LZMA_PREPARE,
+		SEQ_LZMA_RUN,
+		SEQ_COPY
+	} sequence;
+
+	/* Next position after decoding the compressed size of the chunk. */
+	enum lzma2_seq next_sequence;
+
+	/* Uncompressed size of LZMA chunk (2 MiB at maximum) */
+	uint32_t uncompressed;
+
+	/*
+	 * Compressed size of LZMA chunk or compressed/uncompressed
+	 * size of uncompressed chunk (64 KiB at maximum)
+	 */
+	uint32_t compressed;
+
+	/*
+	 * True if dictionary reset is needed. This is false before
+	 * the first chunk (LZMA or uncompressed).
+	 */
+	bool need_dict_reset;
+
+	/*
+	 * True if new LZMA properties are needed. This is false
+	 * before the first LZMA chunk.
+	 */
+	bool need_props;
+};
+
 struct xz_dec_lzma2 {
-	/* LZMA2 */
-	struct {
-		/* Position in xz_dec_lzma2_run(). */
-		enum lzma2_seq {
-			SEQ_CONTROL,
-			SEQ_UNCOMPRESSED_1,
-			SEQ_UNCOMPRESSED_2,
-			SEQ_COMPRESSED_0,
-			SEQ_COMPRESSED_1,
-			SEQ_PROPERTIES,
-			SEQ_LZMA_PREPARE,
-			SEQ_LZMA_RUN,
-			SEQ_COPY
-		} sequence;
-
-		/*
-		 * Next position after decoding the compressed size of
-		 * the chunk.
-		 */
-		enum lzma2_seq next_sequence;
-
-		/* Uncompressed size of LZMA chunk (2 MiB at maximum) */
-		uint32_t uncompressed;
-
-		/*
-		 * Compressed size of LZMA chunk or compressed/uncompressed
-		 * size of uncompressed chunk (64 KiB at maximum)
-		 */
-		uint32_t compressed;
-
-		/*
-		 * True if dictionary reset is needed. This is false before
-		 * the first chunk (LZMA or uncompressed).
-		 */
-		bool need_dict_reset;
-
-		/*
-		 * True if new LZMA properties are needed. This is false
-		 * before the first LZMA chunk.
-		 */
-		bool need_props;
-	} lzma2;
+	/*
+	 * The order below is important on x86 to reduce code size and
+	 * it shouldn't hurt on other platforms. Everything up to and
+	 * including lzma.pos_mask are in the first 128 bytes on x86-32,
+	 * which allows using smaller instructions to access those
+	 * variables. On x86-64, fewer variables fit into the first 128
+	 * bytes, but this is still the best order without sacrificing
+	 * the readability by splitting the structures.
+	 */
+	struct rc_dec rc;
+	struct dictionary dict;
+	struct lzma2_dec lzma2;
+	struct lzma_dec lzma;
 
 	/*
 	 * Temporary buffer which holds small number of input bytes between
@@ -263,10 +273,6 @@ struct xz_dec_lzma2 {
 		uint32_t size;
 		uint8_t buf[3 * LZMA_IN_REQUIRED];
 	} temp;
-
-	struct dictionary dict;
-	struct rc_dec rc;
-	struct lzma_dec lzma;
 };
 
 /**************