[x86_64] Introduce insvti_highpart define_insn_and_split.

This is a repost/respin of a patch that was conditionally approved:
https://gcc.gnu.org/pipermail/gcc-patches/2023-January/609470.html

This patch adds a convenient post-reload splitter for setting/updating
the highpart of a TImode variable, using i386's previously added
split_double_concat infrastructure.

For the new test case below:

__int128 foo(__int128 x, unsigned long long y)
{
  __int128 t = (__int128)y << 64;
  __int128 r = (x & ~0ull) | t;
  return r;
}

mainline GCC with -O2 currently generates:

foo:    movq    %rdi, %rcx
        xorl    %eax, %eax
        xorl    %edi, %edi
        orq     %rcx, %rax
        orq     %rdi, %rdx
        ret

with this patch, GCC instead now generates the much better:

foo:	movq    %rdi, %rcx
        movq    %rcx, %rax
        ret

It turns out that the -m32 equivalent of this testcase, already
avoids using explict orl/xor instructions, as it gets optimized
(in combine) by a completely different path.  Given that this idiom
isn't seen in 32-bit code (so this pattern doesn't match with -m32),
and also that the shorter 32-bit AND bitmask is represented as a
CONST_INT rather than a CONST_WIDE_INT, this new define_insn_and_split
is implemented for just TARGET_64BIT rather than contort a "generic"
implementation using DWI mode iterators.

2023-05-08  Roger Sayle  <roger@nextmovesoftware.com>
	    Uros Bizjak  <ubizjak@gmail.com>

gcc/ChangeLog
	* config/i386/i386.md (any_or_plus): Move definition earlier.
	(*insvti_highpart_1): New define_insn_and_split to overwrite
	(insv) the highpart of a TImode register/memory.

gcc/testsuite/ChangeLog
	* gcc.target/i386/insvti_highpart-1.c: New test case.

2 files changed, 38 insertions, 1 deletions

diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index cf90867..5a064f3 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -3479,6 +3479,32 @@
   "mov{b}\t{%h1, %h0|%h0, %h1}"
   [(set_attr "type" "imov")
    (set_attr "mode" "QI")])
+
+(define_code_iterator any_or_plus [plus ior xor])
+
+(define_insn_and_split "*insvti_highpart_1"
+  [(set (match_operand:TI 0 "nonimmediate_operand" "=ro,r,r,&r")
+	(any_or_plus:TI
+	  (and:TI
+	    (match_operand:TI 1 "nonimmediate_operand" "r,m,r,m")
+	    (match_operand:TI 3 "const_scalar_int_operand" "n,n,n,n"))
+	  (ashift:TI
+	    (zero_extend:TI
+	      (match_operand:DI 2 "nonimmediate_operand" "r,r,m,m"))
+	    (const_int 64))))]
+  "TARGET_64BIT
+   && CONST_WIDE_INT_P (operands[3])
+   && CONST_WIDE_INT_NUNITS (operands[3]) == 2
+   && CONST_WIDE_INT_ELT (operands[3], 0) == -1
+   && CONST_WIDE_INT_ELT (operands[3], 1) == 0"
+  "#"
+  "&& reload_completed"
+  [(const_int 0)]
+{
+  operands[4] = gen_lowpart (DImode, operands[1]);
+  split_double_concat (TImode, operands[0], operands[4], operands[2]);
+  DONE;
+})
 
 ;; Floating point push instructions.
 
@@ -11573,7 +11599,6 @@
    (set_attr "mode" "QI")])
 
 ;; Split DST = (HI<<32)|LO early to minimize register usage.
-(define_code_iterator any_or_plus [plus ior xor])
 (define_insn_and_split "*concat<mode><dwi>3_1"
   [(set (match_operand:<DWI> 0 "nonimmediate_operand" "=ro,r")
 	(any_or_plus:<DWI>
diff --git a/gcc/testsuite/gcc.target/i386/insvti_highpart-1.c b/gcc/testsuite/gcc.target/i386/insvti_highpart-1.c
new file mode 100644
index 0000000..4ae9ccf
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/insvti_highpart-1.c
@@ -0,0 +1,12 @@
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-O2" } */
+
+__int128 foo(__int128 x, unsigned long long y)
+{
+  __int128 t = (__int128)y << 64;
+  __int128 r = (x & ~0ull) | t;
+  return r;
+}
+
+/* { dg-final { scan-assembler-not "xorl" } } */
+/* { dg-final { scan-assembler-not "orq" } } */