tcg/tci: Change encoding to uint32_t units

This removes all of the problems with unaligned accesses
to the bytecode stream.

With an 8-bit opcode at the bottom, we have 24 bits remaining,
which are generally split into 6 4-bit slots.  This fits well
with the maximum length opcodes, e.g. INDEX_op_add2_i32, which
have 6 register operands.

We have, in previous patches, rearranged things such that there
are no operations with a label which have more than one other
operand.  Which leaves us with a 20-bit field in which to encode
a label, giving us a maximum TB size of 512k -- easily large.

Change the INDEX_op_tci_movi_{i32,i64} opcodes to tci_mov[il].
The former puts the immediate in the upper 20 bits of the insn,
like we do for the label displacement.  The later uses a label
to reference an entry in the constant pool.  Thus, in the worst
case we still have a single memory reference for any constant,
but now the constants are out-of-line of the bytecode and can
be shared between different moves saving space.

Change INDEX_op_call to use a label to reference a pair of
pointers in the constant pool.  This removes the only slightly
dodgy link with the layout of struct TCGHelperInfo.

The re-encode cannot be done in pieces.

Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

1 files changed, 5 insertions, 15 deletions

diff --git a/tcg/tci/README b/tcg/tci/README
index 9bb7d7a5d3..f72a40a395 100644
--- a/tcg/tci/README
+++ b/tcg/tci/README
@@ -23,10 +23,12 @@ This is what TCI (Tiny Code Interpreter) does.
 Like each TCG host frontend, TCI implements the code generator in
 tcg-target.c.inc, tcg-target.h. Both files are in directory tcg/tci.
 
-The additional file tcg/tci.c adds the interpreter.
+The additional file tcg/tci.c adds the interpreter and disassembler.
 
-The bytecode consists of opcodes (same numeric values as those used by
-TCG), command length and arguments of variable size and number.
+The bytecode consists of opcodes (with only a few exceptions, with
+the same same numeric values and semantics as used by TCG), and up
+to six arguments packed into a 32-bit integer.  See comments in tci.c
+for details on the encoding.
 
 3) Usage
 
@@ -39,11 +41,6 @@ suggest using this option. Setting it automatically would need
 additional code in configure which must be fixed when new native TCG
 implementations are added.
 
-System emulation should work on any 32 or 64 bit host.
-User mode emulation might work. Maybe a new linker script (*.ld)
-is needed. Byte order might be wrong (on big endian hosts)
-and need fixes in configure.
-
 For hosts with native TCG, the interpreter TCI can be enabled by
 
         configure --enable-tcg-interpreter
@@ -118,13 +115,6 @@ u1 = linux-user-test works
   in the interpreter. These opcodes raise a runtime exception, so it is
   possible to see where code must be added.
 
-* The pseudo code is not optimized and still ugly. For hosts with special
-  alignment requirements, it needs some fixes (maybe aligned bytecode
-  would also improve speed for hosts which support byte alignment).
-
-* A better disassembler for the pseudo code would be nice (a very primitive
-  disassembler is included in tcg-target.c.inc).
-
 * It might be useful to have a runtime option which selects the native TCG
   or TCI, so QEMU would have to include two TCGs. Today, selecting TCI
   is a configure option, so you need two compilations of QEMU.