middle-end/61747 - conditional move expansion and constants

When expanding a COND_EXPR or a VEC_COND_EXPR the x86 backend for
example tries to match FP min/max instructions.  But this only
works when it can see the equality of the comparison and selected
operands.  This breaks in both prepare_cmp_insn and vector_compare_rtx
where the former forces expensive constants to a register and the
latter performs legitimization.  The patch below fixes this in
the caller preserving former equalities.

	PR middle-end/61747
	* internal-fn.cc (expand_vec_cond_optab_fn): When the
	value operands are equal to the original comparison operands
	preserve that equality by re-using the comparison expansion.
	* optabs.cc (emit_conditional_move): When the value operands
	are equal to the comparison operands and would be forced to
	a register by prepare_cmp_insn do so earlier, preserving the
	equality.

	* g++.target/i386/pr61747.C: New testcase.

gcc/internal-fn.cc

@@ -3020,8 +3020,21 @@ expand_vec_cond_optab_fn (internal_fn, gcall *stmt, convert_optab optab)
   icode = convert_optab_handler (optab, mode, cmp_op_mode);
   rtx comparison
     = vector_compare_rtx (VOIDmode, tcode, op0a, op0b, unsignedp, icode, 4);
-  rtx rtx_op1 = expand_normal (op1);
-  rtx rtx_op2 = expand_normal (op2);
+  /* vector_compare_rtx legitimizes operands, preserve equality when
+     expanding op1/op2.  */
+  rtx rtx_op1, rtx_op2;
+  if (operand_equal_p (op1, op0a))
+    rtx_op1 = XEXP (comparison, 0);
+  else if (operand_equal_p (op1, op0b))
+    rtx_op1 = XEXP (comparison, 1);
+  else
+    rtx_op1 = expand_normal (op1);
+  if (operand_equal_p (op2, op0a))
+    rtx_op2 = XEXP (comparison, 0);
+  else if (operand_equal_p (op2, op0b))
+    rtx_op2 = XEXP (comparison, 1);
+  else
+    rtx_op2 = expand_normal (op2);
 
   rtx target = expand_expr (lhs, NULL_RTX, VOIDmode, EXPAND_WRITE);
   create_output_operand (&ops[0], target, mode);

gcc/optabs.cc

@@ -5119,13 +5119,41 @@ emit_conditional_move (rtx target, struct rtx_comparison comp,
 	  last = get_last_insn ();
 	  do_pending_stack_adjust ();
 	  machine_mode cmpmode = comp.mode;
+	  rtx orig_op0 = XEXP (comparison, 0);
+	  rtx orig_op1 = XEXP (comparison, 1);
+	  rtx op2p = op2;
+	  rtx op3p = op3;
+	  /* If we are optimizing, force expensive constants into a register
+	     but preserve an eventual equality with op2/op3.  */
+	  if (CONSTANT_P (orig_op0) && optimize
+	      && (rtx_cost (orig_op0, mode, COMPARE, 0,
+			    optimize_insn_for_speed_p ())
+		  > COSTS_N_INSNS (1))
+	      && can_create_pseudo_p ())
+	    {
+	      if (rtx_equal_p (orig_op0, op2))
+		op2p = XEXP (comparison, 0) = force_reg (cmpmode, orig_op0);
+	      else if (rtx_equal_p (orig_op0, op3))
+		op3p = XEXP (comparison, 0) = force_reg (cmpmode, orig_op0);
+	    }
+	  if (CONSTANT_P (orig_op1) && optimize
+	      && (rtx_cost (orig_op1, mode, COMPARE, 0,
+			    optimize_insn_for_speed_p ())
+		  > COSTS_N_INSNS (1))
+	      && can_create_pseudo_p ())
+	    {
+	      if (rtx_equal_p (orig_op1, op2))
+		op2p = XEXP (comparison, 1) = force_reg (cmpmode, orig_op1);
+	      else if (rtx_equal_p (orig_op1, op3))
+		op3p = XEXP (comparison, 1) = force_reg (cmpmode, orig_op1);
+	    }
 	  prepare_cmp_insn (XEXP (comparison, 0), XEXP (comparison, 1),
 			    GET_CODE (comparison), NULL_RTX, unsignedp,
 			    OPTAB_WIDEN, &comparison, &cmpmode);
 	  if (comparison)
 	    {
 	       rtx res = emit_conditional_move_1 (target, comparison,
-						  op2, op3, mode);
+						  op2p, op3p, mode);
 	       if (res != NULL_RTX)
 		 return res;
 	    }

gcc/testsuite/g++.target/i386/pr61747.C

@@ -0,0 +1,42 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target c++11 } */
+/* { dg-options "-O2 -msse4.1 -mfpmath=sse" } */
+
+typedef float __attribute__( ( vector_size( 16 ) ) ) float32x4_t;
+
+template<typename V1>
+V1 vmax(V1 a, V1 b) {
+    return (a>b) ? a : b;
+}
+
+template<typename V1>
+V1 vmin(V1 a, V1 b) {
+    return (a<b) ? a : b;
+}
+
+float foo(float a, float b, float c) {
+    return vmin(vmax(a,b),c);
+}
+
+float32x4_t foo(float32x4_t a, float32x4_t b, float32x4_t c) {
+    return vmin(vmax(a,b),c);
+}
+
+template<typename Float>
+Float bart(Float a) { 
+    constexpr Float zero{0.f};
+    constexpr Float it = zero+4.f;
+    constexpr Float zt = zero-3.f;
+    return vmin(vmax(a,zt),it);
+}
+
+float bar(float a) {
+    return bart(a);
+}
+
+float32x4_t bar(float32x4_t a) {
+    return bart(a);
+}
+
+/* { dg-final { scan-assembler-times "min" 4 } } */
+/* { dg-final { scan-assembler-times "max" 4 } } */