Canonicalize (vec_merge (fma op2 op1 op3) op1 mask) to (vec_merge (fma op1 op2 op3) op1 mask).

For x86 masked fma, there're 2 rtl representations
1) (vec_merge (fma op2 op1 op3) op1 mask)
2) (vec_merge (fma op1 op2 op3) op1 mask).

 5894(define_insn "<avx512>_fmadd_<mode>_mask<round_name>"
 5895  [(set (match_operand:VFH_AVX512VL 0 "register_operand" "=v,v")
 5896        (vec_merge:VFH_AVX512VL
 5897          (fma:VFH_AVX512VL
 5898            (match_operand:VFH_AVX512VL 1 "nonimmediate_operand" "0,0")
 5899            (match_operand:VFH_AVX512VL 2 "<round_nimm_predicate>" "<round_constraint>,v")
 5900            (match_operand:VFH_AVX512VL 3 "<round_nimm_predicate>" "v,<round_constraint>"))
 5901          (match_dup 1)
 5902          (match_operand:<avx512fmaskmode> 4 "register_operand" "Yk,Yk")))]
 5903  "TARGET_AVX512F && <round_mode_condition>"
 5904  "@
 5905   vfmadd132<ssemodesuffix>\t{<round_op5>%2, %3, %0%{%4%}|%0%{%4%}, %3, %2<round_op5>}
 5906   vfmadd213<ssemodesuffix>\t{<round_op5>%3, %2, %0%{%4%}|%0%{%4%}, %2, %3<round_op5>}"
 5907  [(set_attr "type" "ssemuladd")
 5908   (set_attr "prefix" "evex")
 5909   (set_attr "mode" "<MODE>")])

Here op1 has constraint "0", and the scecond op1 is (match_dup 1),
we once tried to replace it with (match_operand:M 5
"nonimmediate_operand" "0")) to enable more flexibility for pattern
match and recog, but it triggered an ICE in reload(reload can handle
at most one perand with "0" constraint).

So we need either add 2 patterns in the backend or just do the
canonicalization in the middle-end.

gcc/ChangeLog:

	PR middle-end/117072
	* combine.cc (maybe_swap_commutative_operands):
	Canonicalize (vec_merge (fma op2 op1 op3) op1 mask)
	to (vec_merge (fma op1 op2 op3) op1 mask).

gcc/combine.cc

@@ -5656,6 +5656,31 @@ maybe_swap_commutative_operands (rtx x)
       SUBST (XEXP (x, 1), temp);
     }
 
+  /* Canonicalize (vec_merge (fma op2 op1 op3) op1 mask) to
+     (vec_merge (fma op1 op2 op3) op1 mask).  */
+  if (GET_CODE (x) == VEC_MERGE
+      && GET_CODE (XEXP (x, 0)) == FMA)
+    {
+      rtx fma_op1 = XEXP (XEXP (x, 0), 0);
+      rtx fma_op2 = XEXP (XEXP (x, 0), 1);
+      rtx masked_op = XEXP (x, 1);
+      if (rtx_equal_p (masked_op, fma_op2))
+	{
+	  if (GET_CODE (fma_op1) == NEG)
+	    {
+	      /* Keep the negate canonicalized to the first operand.  */
+	      fma_op1 = XEXP (fma_op1, 0);
+	      SUBST (XEXP (XEXP (XEXP (x, 0), 0), 0), fma_op2);
+	      SUBST (XEXP (XEXP (x, 0), 1), fma_op1);
+	    }
+	  else
+	    {
+	      SUBST (XEXP (XEXP (x, 0), 0), fma_op2);
+	      SUBST (XEXP (XEXP (x, 0), 1), fma_op1);
+	    }
+	}
+    }
+
   unsigned n_elts = 0;
   if (GET_CODE (x) == VEC_MERGE
       && CONST_INT_P (XEXP (x, 2))