tree-ssa-math-opts.c (convert_mult_to_fma): Do not verify that the target has the...

	* tree-ssa-math-opts.c (convert_mult_to_fma): Do not verify
	that the target has the exact fma operation that we matched.

From-SVN: r166611

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 542d95953d657d5cf5f6cac7e35bdf0e36801523..2cdcaf204f01b86e941edb2120101e3936d17bb9 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2010-11-11  Richard Henderson  <rth@redhat.com>
+
+       * tree-ssa-math-opts.c (convert_mult_to_fma): Do not verify
+       that the target has the exact fma operation that we matched.
+
 2010-11-11  Joseph Myers  <joseph@codesourcery.com>
 
        * reginfo.c (fix_register): Avoid inserting English word in

diff --git a/gcc/tree-ssa-math-opts.c b/gcc/tree-ssa-math-opts.c
index 28401502aa9b306ceedeecfd6cd4d3404c618376..a2dfac6bb482e634de617ff8d07f98ea17f8f11c 100644 (file)
--- a/gcc/tree-ssa-math-opts.c
+++ b/gcc/tree-ssa-math-opts.c
@@ -1531,7 +1531,6 @@ convert_mult_to_fma (gimple mul_stmt)
       enum tree_code use_code;
       tree result = mul_result;
       bool negate_p = false;
-      optab opt;
 
       use_stmt = USE_STMT (use_p);
 
@@ -1574,32 +1573,31 @@ convert_mult_to_fma (gimple mul_stmt)
          negate_p = true;
        }
 
-      /* Determine if the target supports the exact form we found.  */
       switch (use_code)
        {
        case MINUS_EXPR:
-         if (gimple_assign_rhs1 (use_stmt) == result)
-           {
-             opt = negate_p ? fnms_optab : fms_optab;
-             break;
-           }
-         negate_p = !negate_p;
-         /* FALLTHRU */
-
+         if (gimple_assign_rhs2 (use_stmt) == result)
+           negate_p = !negate_p;
+         break;
        case PLUS_EXPR:
-         opt = negate_p ? fnma_optab : fma_optab;
          break;
-
        default:
          /* FMA can only be formed from PLUS and MINUS.  */
          return false;
        }
-      if (optab_handler (opt, TYPE_MODE (type)) == CODE_FOR_nothing)
-       return false;
 
       /* We can't handle a * b + a * b.  */
       if (gimple_assign_rhs1 (use_stmt) == gimple_assign_rhs2 (use_stmt))
        return false;
+
+      /* While it is possible to validate whether or not the exact form
+        that we've recognized is available in the backend, the assumption
+        is that the transformation is never a loss.  For instance, suppose
+        the target only has the plain FMA pattern available.  Consider
+        a*b-c -> fma(a,b,-c): we've exchanged MUL+SUB for FMA+NEG, which
+        is still two operations.  Consider -(a*b)-c -> fma(-a,b,-c): we
+        still have 3 operations, but in the FMA form the two NEGs are
+        independant and could be run in parallel.  */
     }
 
   FOR_EACH_IMM_USE_STMT (use_stmt, imm_iter, mul_result)