PR target/113690: Remove TImode REG_EQUAL notes in STV.

This patch fixes PR target/113690, an ICE-on-valid regression on x86_64
that exhibits with a specific combination of command line options.  The
cause is that x86's scalar-to-vector pass converts a chain of instructions
from TImode to V1TImode, but fails to appropriately update or delete the
attached REG_EQUAL note.  This implements Uros' recommendation of removing
these notes.  For convenience, this code (re)factors the logic to convert
a TImode constant into a V1TImode constant vector into a subroutine and
reuses it.

For the record, STV is actually doing something useful in this strange
testcase,  GCC with -O2 -fno-dce -fno-forward-propagate -fno-split-wide-types
-funroll-loops generates:

foo:	movl    $v, %eax
        pxor    %xmm0, %xmm0
        movaps  %xmm0, 48(%rax)
        movaps  %xmm0, (%rax)
        movaps  %xmm0, 16(%rax)
        movaps  %xmm0, 32(%rax)
        ret

With the addition of -mno-stv (to disable the patched code) it gives:

foo:	movl    $v, %eax
        movq    $0, 48(%rax)
        movq    $0, 56(%rax)
        movq    $0, (%rax)
        movq    $0, 8(%rax)
        movq    $0, 16(%rax)
        movq    $0, 24(%rax)
        movq    $0, 32(%rax)
        movq    $0, 40(%rax)
        ret

2024-02-07  Roger Sayle  <roger@nextmovesoftware.com>
	    Uros Bizjak  <ubizjak@gmail.com>

gcc/ChangeLog
	PR target/113690
	* config/i386/i386-features.cc (timode_convert_cst): New helper
	function to convert a TImode CONST_SCALAR_INT_P to a V1TImode
	CONST_VECTOR.
	(timode_scalar_chain::convert_op): Use timode_convert_cst.
	(timode_scalar_chain::convert_insn): Delete REG_EQUAL notes.
	Use timode_convert_cst.

gcc/testsuite/ChangeLog
	PR target/113690
	* gcc.target/i386/pr113690.c: New test case.

2 files changed, 32 insertions, 22 deletions

diff --git a/gcc/config/i386/i386-features.cc b/gcc/config/i386/i386-features.cc
index e0b9615..f1b1cf2 100644
--- a/gcc/config/i386/i386-features.cc
+++ b/gcc/config/i386/i386-features.cc
@@ -1749,6 +1749,19 @@ timode_scalar_chain::fix_debug_reg_uses (rtx reg)
     }
 }
 
+/* Helper function to convert immediate constant X to V1TImode.  */
+static rtx
+timode_convert_cst (rtx x)
+{
+  /* Prefer all ones vector in case of -1.  */
+  if (constm1_operand (x, TImode))
+    return CONSTM1_RTX (V1TImode);
+
+  rtx *v = XALLOCAVEC (rtx, 1);
+  v[0] = x;
+  return gen_rtx_CONST_VECTOR (V1TImode, gen_rtvec_v (1, v));
+}
+
 /* Convert operand OP in INSN from TImode to V1TImode.  */
 
 void
@@ -1775,18 +1788,8 @@ timode_scalar_chain::convert_op (rtx *op, rtx_insn *insn)
     }
   else if (CONST_SCALAR_INT_P (*op))
     {
-      rtx vec_cst;
       rtx tmp = gen_reg_rtx (V1TImode);
-
-      /* Prefer all ones vector in case of -1.  */
-      if (constm1_operand (*op, TImode))
-	vec_cst = CONSTM1_RTX (V1TImode);
-      else
-	{
-	  rtx *v = XALLOCAVEC (rtx, 1);
-	  v[0] = *op;
-	  vec_cst = gen_rtx_CONST_VECTOR (V1TImode, gen_rtvec_v (1, v));
-	}
+      rtx vec_cst = timode_convert_cst (*op);
 
       if (!standard_sse_constant_p (vec_cst, V1TImode))
 	{
@@ -1827,16 +1830,11 @@ timode_scalar_chain::convert_insn (rtx_insn *insn)
 	}
       if (GET_MODE (dst) == V1TImode)
 	{
-	  tmp = find_reg_equal_equiv_note (insn);
-	  if (tmp)
-	    {
-	      if (GET_MODE (XEXP (tmp, 0)) == TImode)
-		PUT_MODE (XEXP (tmp, 0), V1TImode);
-	      else if (CONST_SCALAR_INT_P (XEXP (tmp, 0)))
-		XEXP (tmp, 0)
-		  = gen_rtx_CONST_VECTOR (V1TImode,
-					  gen_rtvec (1, XEXP (tmp, 0)));
-	    }
+	  /* It might potentially be helpful to convert REG_EQUAL notes,
+	     but for now we just remove them.  */
+	  rtx note = find_reg_equal_equiv_note (insn);
+	  if (note)
+	    remove_note (insn, note);
 	}
       break;
     case MEM:
@@ -1876,7 +1874,7 @@ timode_scalar_chain::convert_insn (rtx_insn *insn)
 	    }
 	  else
 	    {
-	      src = gen_rtx_CONST_VECTOR (V1TImode, gen_rtvec (1, src));
+	      src = timode_convert_cst (src);
 	      src = validize_mem (force_const_mem (V1TImode, src));
 	      use_move = MEM_P (dst);
 	    }
diff --git a/gcc/testsuite/gcc.target/i386/pr113690.c b/gcc/testsuite/gcc.target/i386/pr113690.c
new file mode 100644
index 0000000..23a1108
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr113690.c
@@ -0,0 +1,12 @@
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-O2 -fno-dce -fno-forward-propagate -fno-split-wide-types -funroll-loops" } */
+int i;
+__attribute__((__vector_size__(64))) __int128 v;
+
+void
+foo(void)
+{
+  v <<= 127;
+  __builtin_mul_overflow(0, i, &v[3]);
+  v *= 6;
+}