tcg: Optimize spills of constants

While we can store constants via constrants on INDEX_op_st_i32 et al,
we weren't able to spill constants to backing store.

Add a new backend interface, tcg_out_sti, which may store the constant
(and is allowed to fail).  Rearrange the temp_* helpers so that we only
attempt to directly store a constant when the temp is becoming dead/free.

Signed-off-by: Richard Henderson <rth@twiddle.net>

1 files changed, 91 insertions, 74 deletions

diff --git a/tcg/tcg.c b/tcg/tcg.c
index 154ffe801c..ef8a8556e4 100644
--- a/tcg/tcg.c
+++ b/tcg/tcg.c
@@ -108,6 +108,8 @@ static void tcg_out_op(TCGContext *s, TCGOpcode opc, const TCGArg *args,
                        const int *const_args);
 static void tcg_out_st(TCGContext *s, TCGType type, TCGReg arg, TCGReg arg1,
                        intptr_t arg2);
+static bool tcg_out_sti(TCGContext *s, TCGType type, TCGArg val,
+                        TCGReg base, intptr_t ofs);
 static void tcg_out_call(TCGContext *s, tcg_insn_unit *target);
 static int tcg_target_const_match(tcg_target_long val, TCGType type,
                                   const TCGArgConstraint *arg_ct);
@@ -1680,35 +1682,89 @@ static void temp_allocate_frame(TCGContext *s, int temp)
 
 static void temp_load(TCGContext *, TCGTemp *, TCGRegSet, TCGRegSet);
 
-/* sync register 'reg' by saving it to the corresponding temporary */
-static void tcg_reg_sync(TCGContext *s, TCGReg reg, TCGRegSet allocated_regs)
+/* Mark a temporary as free or dead.  If 'free_or_dead' is negative,
+   mark it free; otherwise mark it dead.  */
+static void temp_free_or_dead(TCGContext *s, TCGTemp *ts, int free_or_dead)
 {
-    TCGTemp *ts = s->reg_to_temp[reg];
+    if (ts->fixed_reg) {
+        return;
+    }
+    if (ts->val_type == TEMP_VAL_REG) {
+        s->reg_to_temp[ts->reg] = NULL;
+    }
+    ts->val_type = (free_or_dead < 0
+                    || ts->temp_local
+                    || temp_idx(s, ts) < s->nb_globals
+                    ? TEMP_VAL_MEM : TEMP_VAL_DEAD);
+}
 
-    tcg_debug_assert(ts->val_type == TEMP_VAL_REG);
-    if (!ts->mem_coherent && !ts->fixed_reg) {
+/* Mark a temporary as dead.  */
+static inline void temp_dead(TCGContext *s, TCGTemp *ts)
+{
+    temp_free_or_dead(s, ts, 1);
+}
+
+/* Sync a temporary to memory. 'allocated_regs' is used in case a temporary
+   registers needs to be allocated to store a constant.  If 'free_or_dead'
+   is non-zero, subsequently release the temporary; if it is positive, the
+   temp is dead; if it is negative, the temp is free.  */
+static void temp_sync(TCGContext *s, TCGTemp *ts,
+                      TCGRegSet allocated_regs, int free_or_dead)
+{
+    if (ts->fixed_reg) {
+        return;
+    }
+    if (!ts->mem_coherent) {
         if (!ts->mem_allocated) {
             temp_allocate_frame(s, temp_idx(s, ts));
-        } else if (ts->indirect_reg) {
-            tcg_regset_set_reg(allocated_regs, ts->reg);
+        }
+        if (ts->indirect_reg) {
+            if (ts->val_type == TEMP_VAL_REG) {
+                tcg_regset_set_reg(allocated_regs, ts->reg);
+            }
             temp_load(s, ts->mem_base,
                       tcg_target_available_regs[TCG_TYPE_PTR],
                       allocated_regs);
         }
-        tcg_out_st(s, ts->type, reg, ts->mem_base->reg, ts->mem_offset);
+        switch (ts->val_type) {
+        case TEMP_VAL_CONST:
+            /* If we're going to free the temp immediately, then we won't
+               require it later in a register, so attempt to store the
+               constant to memory directly.  */
+            if (free_or_dead
+                && tcg_out_sti(s, ts->type, ts->val,
+                               ts->mem_base->reg, ts->mem_offset)) {
+                break;
+            }
+            temp_load(s, ts, tcg_target_available_regs[ts->type],
+                      allocated_regs);
+            /* fallthrough */
+
+        case TEMP_VAL_REG:
+            tcg_out_st(s, ts->type, ts->reg,
+                       ts->mem_base->reg, ts->mem_offset);
+            break;
+
+        case TEMP_VAL_MEM:
+            break;
+
+        case TEMP_VAL_DEAD:
+        default:
+            tcg_abort();
+        }
+        ts->mem_coherent = 1;
+    }
+    if (free_or_dead) {
+        temp_free_or_dead(s, ts, free_or_dead);
     }
-    ts->mem_coherent = 1;
 }
 
 /* free register 'reg' by spilling the corresponding temporary if necessary */
 static void tcg_reg_free(TCGContext *s, TCGReg reg, TCGRegSet allocated_regs)
 {
     TCGTemp *ts = s->reg_to_temp[reg];
-
     if (ts != NULL) {
-        tcg_reg_sync(s, reg, allocated_regs);
-        ts->val_type = TEMP_VAL_MEM;
-        s->reg_to_temp[reg] = NULL;
+        temp_sync(s, ts, allocated_regs, -1);
     }
 }
 
@@ -1778,45 +1834,9 @@ static void temp_load(TCGContext *s, TCGTemp *ts, TCGRegSet desired_regs,
     s->reg_to_temp[reg] = ts;
 }
 
-/* mark a temporary as dead. */
-static inline void temp_dead(TCGContext *s, TCGTemp *ts)
-{
-    if (ts->fixed_reg) {
-        return;
-    }
-    if (ts->val_type == TEMP_VAL_REG) {
-        s->reg_to_temp[ts->reg] = NULL;
-    }
-    ts->val_type = (temp_idx(s, ts) < s->nb_globals || ts->temp_local
-                    ? TEMP_VAL_MEM : TEMP_VAL_DEAD);
-}
-
-/* sync a temporary to memory. 'allocated_regs' is used in case a
-   temporary registers needs to be allocated to store a constant. */
-static void temp_sync(TCGContext *s, TCGTemp *ts, TCGRegSet allocated_regs)
-{
-    if (ts->fixed_reg) {
-        return;
-    }
-    switch (ts->val_type) {
-    case TEMP_VAL_CONST:
-        temp_load(s, ts, tcg_target_available_regs[ts->type], allocated_regs);
-        /* fallthrough */
-    case TEMP_VAL_REG:
-        tcg_reg_sync(s, ts->reg, allocated_regs);
-        break;
-    case TEMP_VAL_DEAD:
-    case TEMP_VAL_MEM:
-        break;
-    default:
-        tcg_abort();
-    }
-}
-
-/* save a temporary to memory. 'allocated_regs' is used in case a
-   temporary registers needs to be allocated to store a constant. */
-static inline void temp_save(TCGContext *s, TCGTemp *ts,
-                             TCGRegSet allocated_regs)
+/* Save a temporary to memory. 'allocated_regs' is used in case a
+   temporary registers needs to be allocated to store a constant.  */
+static void temp_save(TCGContext *s, TCGTemp *ts, TCGRegSet allocated_regs)
 {
 #ifdef USE_LIVENESS_ANALYSIS
     /* ??? Liveness does not yet incorporate indirect bases.  */
@@ -1827,8 +1847,7 @@ static inline void temp_save(TCGContext *s, TCGTemp *ts,
         return;
     }
 #endif
-    temp_sync(s, ts, allocated_regs);
-    temp_dead(s, ts);
+    temp_sync(s, ts, allocated_regs, 1);
 }
 
 /* save globals to their canonical location and assume they can be
@@ -1861,7 +1880,7 @@ static void sync_globals(TCGContext *s, TCGRegSet allocated_regs)
             continue;
         }
 #endif
-        temp_sync(s, ts, allocated_regs);
+        temp_sync(s, ts, allocated_regs, 0);
     }
 }
 
@@ -1905,21 +1924,21 @@ static void tcg_reg_alloc_movi(TCGContext *s, const TCGArg *args,
     val = args[1];
 
     if (ots->fixed_reg) {
-        /* for fixed registers, we do not do any constant
-           propagation */
+        /* For fixed registers, we do not do any constant propagation.  */
         tcg_out_movi(s, ots->type, ots->reg, val);
-    } else {
-        /* The movi is not explicitly generated here */
-        if (ots->val_type == TEMP_VAL_REG) {
-            s->reg_to_temp[ots->reg] = NULL;
-        }
-        ots->val_type = TEMP_VAL_CONST;
-        ots->val = val;
+        return;
     }
-    if (NEED_SYNC_ARG(0)) {
-        temp_sync(s, ots, s->reserved_regs);
+
+    /* The movi is not explicitly generated here.  */
+    if (ots->val_type == TEMP_VAL_REG) {
+        s->reg_to_temp[ots->reg] = NULL;
     }
-    if (IS_DEAD_ARG(0)) {
+    ots->val_type = TEMP_VAL_CONST;
+    ots->val = val;
+    ots->mem_coherent = 0;
+    if (NEED_SYNC_ARG(0)) {
+        temp_sync(s, ots, s->reserved_regs, IS_DEAD_ARG(0));
+    } else if (IS_DEAD_ARG(0)) {
         temp_dead(s, ots);
     }
 }
@@ -2004,7 +2023,7 @@ static void tcg_reg_alloc_mov(TCGContext *s, const TCGOpDef *def,
         ots->mem_coherent = 0;
         s->reg_to_temp[ots->reg] = ots;
         if (NEED_SYNC_ARG(0)) {
-            tcg_reg_sync(s, ots->reg, allocated_regs);
+            temp_sync(s, ots, allocated_regs, 0);
         }
     }
 }
@@ -2163,9 +2182,8 @@ static void tcg_reg_alloc_op(TCGContext *s,
             tcg_out_mov(s, ts->type, ts->reg, reg);
         }
         if (NEED_SYNC_ARG(i)) {
-            tcg_reg_sync(s, reg, allocated_regs);
-        }
-        if (IS_DEAD_ARG(i)) {
+            temp_sync(s, ts, allocated_regs, IS_DEAD_ARG(i));
+        } else if (IS_DEAD_ARG(i)) {
             temp_dead(s, ts);
         }
     }
@@ -2298,9 +2316,8 @@ static void tcg_reg_alloc_call(TCGContext *s, int nb_oargs, int nb_iargs,
             ts->mem_coherent = 0;
             s->reg_to_temp[reg] = ts;
             if (NEED_SYNC_ARG(i)) {
-                tcg_reg_sync(s, reg, allocated_regs);
-            }
-            if (IS_DEAD_ARG(i)) {
+                temp_sync(s, ts, allocated_regs, IS_DEAD_ARG(i));
+            } else if (IS_DEAD_ARG(i)) {
                 temp_dead(s, ts);
             }
         }