Merge remote-tracking branch 'afaerber/tags/qom-cpu-for-anthony' into staging

[qemu.git] / tcg / README

diff --git a/tcg/README b/tcg/README
index ec1ac79375aa8911497a24147ab45f4cadcd1a39..063aeb95eadefbb52762135b2f71969787e32397 100644 (file)
--- a/tcg/README
+++ b/tcg/README
@@ -14,6 +14,10 @@ the emulated architecture. As TCG started as a generic C backend used
 for cross compiling, it is assumed that the TCG target is different
 from the host, although it is never the case for QEMU.
 
+In this document, we use "guest" to specify what architecture we are
+emulating; "target" always means the TCG target, the machine on which
+we are running QEMU.
+
 A TCG "function" corresponds to a QEMU Translated Block (TB).
 
 A TCG "temporary" is a variable only live in a basic
@@ -361,7 +365,25 @@ Write 8, 16, 32 or 64 bits to host memory.
 All this opcodes assume that the pointed host memory doesn't correspond
 to a global. In the latter case the behaviour is unpredictable.
 
-********* 64-bit target on 32-bit host support
+********* Multiword arithmetic support
+
+* add2_i32/i64 t0_low, t0_high, t1_low, t1_high, t2_low, t2_high
+* sub2_i32/i64 t0_low, t0_high, t1_low, t1_high, t2_low, t2_high
+
+Similar to add/sub, except that the double-word inputs T1 and T2 are
+formed from two single-word arguments, and the double-word output T0
+is returned in two single-word outputs.
+
+* mulu2_i32/i64 t0_low, t0_high, t1, t2
+
+Similar to mul, except two unsigned inputs T1 and T2 yielding the full
+double-word product T0.  The later is returned in two single-word outputs.
+
+* muls2_i32/i64 t0_low, t0_high, t1, t2
+
+Similar to mulu2, except the two inputs T1 and T2 are signed.
+
+********* 64-bit guest on 32-bit host support
 
 The following opcodes are internal to TCG.  Thus they are to be implemented by
 32-bit host code generators, but are not to be emitted by guest translators.
@@ -372,18 +394,6 @@ They are emitted as needed by inline functions within "tcg-op.h".
 Similar to brcond, except that the 64-bit values T0 and T1
 are formed from two 32-bit arguments.
 
-* add2_i32 t0_low, t0_high, t1_low, t1_high, t2_low, t2_high
-* sub2_i32 t0_low, t0_high, t1_low, t1_high, t2_low, t2_high
-
-Similar to add/sub, except that the 64-bit inputs T1 and T2 are
-formed from two 32-bit arguments, and the 64-bit output T0
-is returned in two 32-bit outputs.
-
-* mulu2_i32 t0_low, t0_high, t1, t2
-
-Similar to mul, except two 32-bit (unsigned) inputs T1 and T2 yielding
-the full 64-bit product T0.  The later is returned in two 32-bit outputs.
-
 * setcond2_i32 dest, t1_low, t1_high, t2_low, t2_high, cond
 
 Similar to setcond, except that the 64-bit values T1 and T2 are
@@ -515,9 +525,9 @@ register.
   a better generated code, but it reduces the memory usage of TCG and
   the speed of the translation.
 
-- Don't hesitate to use helpers for complicated or seldom used target
+- Don't hesitate to use helpers for complicated or seldom used guest
   instructions. There is little performance advantage in using TCG to
-  implement target instructions taking more than about twenty TCG
+  implement guest instructions taking more than about twenty TCG
   instructions. Note that this rule of thumb is more applicable to
   helpers doing complex logic or arithmetic, where the C compiler has
   scope to do a good job of optimisation; it is less relevant where
@@ -525,9 +535,9 @@ register.
   inline TCG may still be faster for longer sequences.
 
 - The hard limit on the number of TCG instructions you can generate
-  per target instruction is set by MAX_OP_PER_INSTR in exec-all.h --
+  per guest instruction is set by MAX_OP_PER_INSTR in exec-all.h --
   you cannot exceed this without risking a buffer overrun.
 
 - Use the 'discard' instruction if you know that TCG won't be able to
   prove that a given global is "dead" at a given program point. The
-  x86 target uses it to improve the condition codes optimisation.
+  x86 guest uses it to improve the condition codes optimisation.