[Qemu-devel] [PATCH 3/3] tcg/arm: improve constant loading

[Aurelien Jarno]

Improve constant loading in two ways:
- On all ARM versions, it's possible to load 0xffffff00 = -0x100 using
  the mvn rd, #0. Fix the conditions.
- On <= ARMv6 versions, where movw and movt are not available, load the
  constants using mov and orr with rotations depending on the constant
  to load. This is very useful for example to load constants where the
  low byte is 0. This reduce the generated code size by about 7%.

Also fix the coding style at the same time.

Cc: Andrzej Zaborowski <address@hidden>
Signed-off-by: Aurelien Jarno <address@hidden>
---
 tcg/arm/tcg-target.c |   39 +++++++++++++++++++++------------------
 1 files changed, 21 insertions(+), 18 deletions(-)

diff --git a/tcg/arm/tcg-target.c b/tcg/arm/tcg-target.c
index 08c44c1..1eb5605 100644
--- a/tcg/arm/tcg-target.c
+++ b/tcg/arm/tcg-target.c
@@ -406,35 +406,38 @@ static inline void tcg_out_dat_imm(TCGContext *s,
 }
 
 static inline void tcg_out_movi32(TCGContext *s,
-                int cond, int rd, int32_t arg)
+                int cond, int rd, uint32_t arg)
 {
     /* TODO: This is very suboptimal, we can easily have a constant
      * pool somewhere after all the instructions.  */
-
-    if (arg < 0 && arg > -0x100)
-        return tcg_out_dat_imm(s, cond, ARITH_MVN, rd, 0, (~arg) & 0xff);
-
-    if (use_armv7_instructions) {
+    if ((int)arg < 0 && (int)arg >= -0x100) {
+        tcg_out_dat_imm(s, cond, ARITH_MVN, rd, 0, (~arg) & 0xff);
+    } else if (use_armv7_instructions) {
         /* use movw/movt */
         /* movw */
         tcg_out32(s, (cond << 28) | 0x03000000 | (rd << 12)
                   | ((arg << 4) & 0x000f0000) | (arg & 0xfff));
-        if (arg & 0xffff0000)
+        if (arg & 0xffff0000) {
             /* movt */
             tcg_out32(s, (cond << 28) | 0x03400000 | (rd << 12)
                       | ((arg >> 12) & 0x000f0000) | ((arg >> 16) & 0xfff));
-    } else {
-        tcg_out_dat_imm(s, cond, ARITH_MOV, rd, 0, arg & 0xff);
-        if (arg & 0x0000ff00)
-            tcg_out_dat_imm(s, cond, ARITH_ORR, rd, rd,
-                            ((arg >>  8) & 0xff) | 0xc00);
-        if (arg & 0x00ff0000)
-            tcg_out_dat_imm(s, cond, ARITH_ORR, rd, rd,
-                            ((arg >> 16) & 0xff) | 0x800);
-        if (arg & 0xff000000)
-            tcg_out_dat_imm(s, cond, ARITH_ORR, rd, rd,
-                            ((arg >> 24) & 0xff) | 0x400);
         }
+    } else {
+        int opc = ARITH_MOV;
+        int rn = 0;
+
+        do {
+            int i, rot;
+
+            i = ctz32(arg) & ~1;
+            rot = ((32 - i) << 7) & 0xf00;
+            tcg_out_dat_imm(s, cond, opc, rd, rn, ((arg >> i) & 0xff) | rot);
+            arg &= ~(0xff << i);
+
+            opc = ARITH_ORR;
+            rn = rd;
+        } while (arg);
+    }
 }
 
 static inline void tcg_out_mul32(TCGContext *s,
-- 
1.7.2.3