commit faa2e10045ef82f4a1a24a7f69e285736143b469
author Richard Henderson <richard.henderson@linaro.org> Thu Aug 26 09:03:59 2021 -0700
committer Richard Henderson <richard.henderson@linaro.org> Thu Oct 28 20:55:07 2021 -0700
tree 28093111895c2b3829c30ccb9d6d8aab2caa3a0b
parent 18cf3d07a2556700895c626754937e90f8e972cf

tcg/optimize: Stop forcing z_mask to "garbage" for 32-bit values

This "garbage" setting pre-dates the addition of the type
changing opcodes INDEX_op_ext_i32_i64, INDEX_op_extu_i32_i64,
and INDEX_op_extr{l,h}_i64_i32.

So now we have a definitive points at which to adjust z_mask
to eliminate such bits from the 32-bit operands.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Luis Pires <luis.pires@eldorado.org.br>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

tcg/optimize.c

diff --git a/tcg/optimize.c b/tcg/optimize.c
index e42f5a1..e0abf76 100644
--- a/tcg/optimize.c
+++ b/tcg/optimize.c
@@ -124,10 +124,6 @@
         ti->is_const = true;
         ti->val = ts->val;
         ti->z_mask = ts->val;
-        if (TCG_TARGET_REG_BITS > 32 && ts->type == TCG_TYPE_I32) {
-            /* High bits of a 32-bit quantity are garbage.  */
-            ti->z_mask |= ~0xffffffffull;
-        }
     } else {
         ti->is_const = false;
         ti->z_mask = -1;
@@ -192,7 +188,6 @@
     TCGTemp *src_ts = arg_temp(src);
     TempOptInfo *di;
     TempOptInfo *si;
-    uint64_t z_mask;
     TCGOpcode new_op;
 
     if (ts_are_copies(dst_ts, src_ts)) {
@@ -224,12 +219,7 @@
     op->args[0] = dst;
     op->args[1] = src;
 
-    z_mask = si->z_mask;
-    if (TCG_TARGET_REG_BITS > 32 && new_op == INDEX_op_mov_i32) {
-        /* High bits of the destination are now garbage.  */
-        z_mask |= ~0xffffffffull;
-    }
-    di->z_mask = z_mask;
+    di->z_mask = si->z_mask;
 
     if (src_ts->type == dst_ts->type) {
         TempOptInfo *ni = ts_info(si->next_copy);
@@ -247,9 +237,14 @@
 static bool tcg_opt_gen_movi(OptContext *ctx, TCGOp *op,
                              TCGArg dst, uint64_t val)
 {
-    /* Convert movi to mov with constant temp. */
-    TCGTemp *tv = tcg_constant_internal(ctx->type, val);
+    TCGTemp *tv;
 
+    if (ctx->type == TCG_TYPE_I32) {
+        val = (int32_t)val;
+    }
+
+    /* Convert movi to mov with constant temp. */
+    tv = tcg_constant_internal(ctx->type, val);
     init_ts_info(ctx, tv);
     return tcg_opt_gen_mov(ctx, op, dst, temp_arg(tv));
 }
@@ -721,14 +716,16 @@
     uint64_t z_mask = ctx->z_mask;
 
     /*
-     * 32-bit ops generate 32-bit results.  For the result is zero test
-     * below, we can ignore high bits, but for further optimizations we
-     * need to record that the high bits contain garbage.
+     * 32-bit ops generate 32-bit results, which for the purpose of
+     * simplifying tcg are sign-extended.  Certainly that's how we
+     * represent our constants elsewhere.  Note that the bits will
+     * be reset properly for a 64-bit value when encountering the
+     * type changing opcodes.
      */
     if (ctx->type == TCG_TYPE_I32) {
-        ctx->z_mask |= MAKE_64BIT_MASK(32, 32);
-        a_mask &= MAKE_64BIT_MASK(0, 32);
-        z_mask &= MAKE_64BIT_MASK(0, 32);
+        a_mask = (int32_t)a_mask;
+        z_mask = (int32_t)z_mask;
+        ctx->z_mask = z_mask;
     }
 
     if (z_mask == 0) {