https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105338
--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
--- gcc/config/i386/i386-expand.cc.jj 2022-04-13 15:42:39.000000000 +0200
+++ gcc/config/i386/i386-expand.cc 2022-04-22 14:18:27.347135185 +0200
@@ -3136,6 +3136,8 @@ ix86_expand_int_movcc (rtx operands[])
bool sign_bit_compare_p = false;
rtx op0 = XEXP (operands[1], 0);
rtx op1 = XEXP (operands[1], 1);
+ rtx op2 = operands[2];
+ rtx op3 = operands[3];
if (GET_MODE (op0) == TImode
|| (GET_MODE (op0) == DImode
@@ -3153,17 +3155,29 @@ ix86_expand_int_movcc (rtx operands[])
|| (op1 == constm1_rtx && (code == GT || code == LE)))
sign_bit_compare_p = true;
+ /* op0 == op1 ? op0 : op3 is equivalent to op0 == op1 ? op1 : op3,
+ but if op1 is a constant, the latter form allows more optimizations,
+ either through the last 2 ops being constant handling, or the one
+ constant and one variable cases. On the other side, for cmov the
+ former might be better as we don't need to load the constant into
+ another register. */
+ if (code == EQ && CONST_INT_P (op1) && rtx_equal_p (op0, op2))
+ op2 = op1;
+ /* Similarly for op0 != op1 ? op2 : op0 and op0 != op1 ? op2 : op1. */
+ else if (code == NE && CONST_INT_P (op1) && rtx_equal_p (op0, op3))
+ op3 = op1;
+
/* Don't attempt mode expansion here -- if we had to expand 5 or 6
HImode insns, we'd be swallowed in word prefix ops. */
if ((mode != HImode || TARGET_FAST_PREFIX)
&& (mode != (TARGET_64BIT ? TImode : DImode))
- && CONST_INT_P (operands[2])
- && CONST_INT_P (operands[3]))
+ && CONST_INT_P (op2)
+ && CONST_INT_P (op3))
{
rtx out = operands[0];
- HOST_WIDE_INT ct = INTVAL (operands[2]);
- HOST_WIDE_INT cf = INTVAL (operands[3]);
+ HOST_WIDE_INT ct = INTVAL (op2);
+ HOST_WIDE_INT cf = INTVAL (op3);
HOST_WIDE_INT diff;
diff = ct - cf;
@@ -3559,6 +3573,9 @@ ix86_expand_int_movcc (rtx operands[])
if (BRANCH_COST (optimize_insn_for_speed_p (), false) <= 2)
return false;
+ operands[2] = op2;
+ operands[3] = op3;
+
/* If one of the two operands is an interesting constant, load a
constant with the above and mask it in with a logical operation. */
fixes the first and last 2 functions, now to look what's going on with the
second and third one...
