The COMPARE RTX has a special conversion procedure that applies only
to DImode double-word operands. Do not convert single-word SImode and
DImode operands for now.

2019-08-15  UroŇ° Bizjak  <ubiz...@gmail.com>

    * config/i386/i386-features.c (general_scalar_chain::convert_insn)
    <case COMPARE>: Revert 2019-08-14 change.
    (convertible_comparison_p): Revert 2019-08-14 change.  Return false
    for (TARGET_64BIT || mode != DImode).

Also update a couple of nearby comments.

Boostrapped and regression tested on x86_64-linux-gnu {,-m32}.

Committed to mainline SVN.

Uros.
Index: config/i386/i386-features.c
===================================================================
--- config/i386/i386-features.c (revision 274504)
+++ config/i386/i386-features.c (working copy)
@@ -1030,11 +1030,11 @@ general_scalar_chain::convert_insn (rtx_insn *insn
     case COMPARE:
       src = SUBREG_REG (XEXP (XEXP (src, 0), 0));
 
-      gcc_assert ((REG_P (src) && GET_MODE (src) == GET_MODE_INNER (vmode))
-                 || (SUBREG_P (src) && GET_MODE (src) == vmode));
+      gcc_assert ((REG_P (src) && GET_MODE (src) == DImode)
+                 || (SUBREG_P (src) && GET_MODE (src) == V2DImode));
 
       if (REG_P (src))
-       subreg = gen_rtx_SUBREG (vmode, src, 0);
+       subreg = gen_rtx_SUBREG (V2DImode, src, 0);
       else
        subreg = copy_rtx_if_shared (src);
       emit_insn_before (gen_vec_interleave_lowv2di (copy_rtx_if_shared 
(subreg),
@@ -1273,8 +1273,12 @@ has_non_address_hard_reg (rtx_insn *insn)
                     (const_int 0 [0])))  */
 
 static bool
-convertible_comparison_p (rtx_insn *insn, enum machine_mode mode)
+convertible_comparison_p (rtx_insn *insn, machine_mode mode)
 {
+  /* ??? Currently convertible for double-word DImode chain only.  */
+  if (TARGET_64BIT || mode != DImode)
+    return false;
+
   if (!TARGET_SSE4_1)
     return false;
 
@@ -1306,12 +1310,12 @@ static bool
 
   if (!SUBREG_P (op1)
       || !SUBREG_P (op2)
-      || GET_MODE (op1) != mode
-      || GET_MODE (op2) != mode
+      || GET_MODE (op1) != SImode
+      || GET_MODE (op2) != SImode
       || ((SUBREG_BYTE (op1) != 0
-          || SUBREG_BYTE (op2) != GET_MODE_SIZE (mode))
+          || SUBREG_BYTE (op2) != GET_MODE_SIZE (SImode))
          && (SUBREG_BYTE (op2) != 0
-             || SUBREG_BYTE (op1) != GET_MODE_SIZE (mode))))
+             || SUBREG_BYTE (op1) != GET_MODE_SIZE (SImode))))
     return false;
 
   op1 = SUBREG_REG (op1);
@@ -1319,13 +1323,13 @@ static bool
 
   if (op1 != op2
       || !REG_P (op1)
-      || GET_MODE (op1) != GET_MODE_WIDER_MODE (mode).else_blk ())
+      || GET_MODE (op1) != DImode)
     return false;
 
   return true;
 }
 
-/* The DImode version of scalar_to_vector_candidate_p.  */
+/* The general version of scalar_to_vector_candidate_p.  */
 
 static bool
 general_scalar_to_vector_candidate_p (rtx_insn *insn, enum machine_mode mode)
@@ -1344,7 +1348,7 @@ general_scalar_to_vector_candidate_p (rtx_insn *in
   if (GET_CODE (src) == COMPARE)
     return convertible_comparison_p (insn, mode);
 
-  /* We are interested in DImode promotion only.  */
+  /* We are interested in "mode" only.  */
   if ((GET_MODE (src) != mode
        && !CONST_INT_P (src))
       || GET_MODE (dst) != mode)

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