expmed.c (expand_smod_pow2): Provide alternate implementations that avoid conditional...

	* expmed.c (expand_smod_pow2): Provide alternate implementations
	that avoid conditional jumps, and choose between them based upon
	the target's rtx_costs.

From-SVN: r83861

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 59f35c1d5dee9135f3881dad4b7cce77e98302f0..36fedf639e9595249cf37915b32a76c1c92cbde8 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2004-06-29  Roger Sayle  <roger@eyesopen.com>
+
+       * expmed.c (expand_smod_pow2): Provide alternate implementations
+       that avoid conditional jumps, and choose between them based upon
+       the target's rtx_costs.
+
 2004-06-29  Andrew Pinski  <apinski@apple.com>
 
        * tree-sra.c: Include expr.h for definition of MOVE_RATIO.

diff --git a/gcc/expmed.c b/gcc/expmed.c
index 6316f9982c0e13be46e7bfba84280696bf2c3325..bb60ba1e832ef3ce70d94f61d8d70f2a836aa5f6 100644 (file)
--- a/gcc/expmed.c
+++ b/gcc/expmed.c
@@ -3064,7 +3064,7 @@ static rtx
 expand_smod_pow2 (enum machine_mode mode, rtx op0, HOST_WIDE_INT d)
 {
   unsigned HOST_WIDE_INT mask;
-  rtx result, temp, label;
+  rtx result, temp, shift, label;
   int logd;
 
   logd = floor_log2 (d);
@@ -3079,17 +3079,42 @@ expand_smod_pow2 (enum machine_mode mode, rtx op0, HOST_WIDE_INT d)
       if (signmask)
        {
          signmask = force_reg (mode, signmask);
-         temp = expand_binop (mode, xor_optab, op0, signmask,
-                              NULL_RTX, 1, OPTAB_LIB_WIDEN);
-         temp = expand_binop (mode, sub_optab, temp, signmask,
-                              NULL_RTX, 0, OPTAB_LIB_WIDEN);
          mask = ((HOST_WIDE_INT) 1 << logd) - 1;
-         temp = expand_binop (mode, and_optab, temp, GEN_INT (mask),
-                              NULL_RTX, 1, OPTAB_LIB_WIDEN);
-         temp = expand_binop (mode, xor_optab, temp, signmask,
-                              NULL_RTX, 1, OPTAB_LIB_WIDEN);
-         temp = expand_binop (mode, sub_optab, temp, signmask,
-                              NULL_RTX, 1, OPTAB_LIB_WIDEN);
+         shift = GEN_INT (GET_MODE_BITSIZE (mode) - logd);
+
+         /* Use the rtx_cost of a LSHIFTRT instruction to determine
+            which instruction sequence to use.  If logical right shifts
+            are expensive the use 2 XORs, 2 SUBs and an AND, otherwise
+            use a LSHIFTRT, 1 ADD, 1 SUB and an AND.  */
+            
+         temp = gen_rtx_LSHIFTRT (mode, result, shift);
+         if (lshr_optab->handlers[mode].insn_code == CODE_FOR_nothing
+             || rtx_cost (temp, SET) > COSTS_N_INSNS (2))
+           {
+             temp = expand_binop (mode, xor_optab, op0, signmask,
+                                  NULL_RTX, 1, OPTAB_LIB_WIDEN);
+             temp = expand_binop (mode, sub_optab, temp, signmask,
+                                  NULL_RTX, 1, OPTAB_LIB_WIDEN);
+             temp = expand_binop (mode, and_optab, temp, GEN_INT (mask),
+                                  NULL_RTX, 1, OPTAB_LIB_WIDEN);
+             temp = expand_binop (mode, xor_optab, temp, signmask,
+                                  NULL_RTX, 1, OPTAB_LIB_WIDEN);
+             temp = expand_binop (mode, sub_optab, temp, signmask,
+                                  NULL_RTX, 1, OPTAB_LIB_WIDEN);
+           }
+         else
+           {
+             signmask = expand_binop (mode, lshr_optab, signmask, shift,
+                                      NULL_RTX, 1, OPTAB_LIB_WIDEN);
+             signmask = force_reg (mode, signmask);
+
+             temp = expand_binop (mode, add_optab, op0, signmask,
+                                  NULL_RTX, 1, OPTAB_LIB_WIDEN);
+             temp = expand_binop (mode, and_optab, temp, GEN_INT (mask),
+                                  NULL_RTX, 1, OPTAB_LIB_WIDEN);
+             temp = expand_binop (mode, sub_optab, temp, signmask,
+                                  NULL_RTX, 1, OPTAB_LIB_WIDEN);
+           }
          return temp;
        }
     }