x86: PR target/103611: Splitter for DST:DI = (HI:SI<<32)|LO:SI.

A common idiom is to create a DImode value from the "concat" of two SImode
values, using "(long long)hi << 32 | (long long)lo", where the operation
may be ior, xor or plus.  On x86, with -m32, the high and low parts of
a DImode register are actually different SImode registers (typically %edx
and %eax) so ideally this idiom should reduce to two move instructions
(or optimally, just clever register allocation).

Unfortunately, GCC currently performs the IOR operation above on -m32,
and worse allocates DImode registers (split to SImode register pairs)
for both the zero extended HI and LO values.

Hence, for test1 from the new test case below:

typedef int __v4si __attribute__ ((__vector_size__ (16)));
long long test1(__v4si v) {
  unsigned int loVal = (unsigned int)v[0];
  unsigned int hiVal = (unsigned int)v[1];
  return (long long)(loVal) | ((long long)(hiVal) << 32);
}

we currently generate (with -m32 -O2 -msse4.1):

test1:	subl    $28, %esp
        pextrd  $1, %xmm0, %eax
        pmovzxdq        %xmm0, %xmm1
        movq    %xmm1, 8(%esp)
        movl    %eax, %edx
        movl    8(%esp), %eax
        orl     12(%esp), %edx
        addl    $28, %esp
        orb     $0, %ah
        ret

with this patch we now generate:

test1:	pextrd  $1, %xmm0, %edx
        movd    %xmm0, %eax
        ret

The fix is to recognize and split the idiom (hi<<32)|zext(lo) prior
to register allocation on !TARGET_64BIT, simplifying this sequence to
"highpart(dst) = hi; lowpart(dst) = lo".

The one minor complication is that sse.md's define_insn for
*vec_extractv4si_0_zext_sse4 can sometimes interfere with this
optimization.  It turns out that on !TARGET_64BIT, the zero_extend:DI
following vec_select:SI isn't free, and this insn gets split back
into multiple instructions during later passes, but too late to
be optimized away by this patch/reload.  Hence the last hunk of
this patch is to restrict *vec_extractv4si_0_zext_sse4 to TARGET_64BIT.
Checking PR target/80286, where *vec_extractv4si_0_zext_sse4 was
first added, this seems reasonable.

2021-12-18  Roger Sayle  <roger@nextmovesoftware.com>
	    Uroš Bizjak  <ubizjak@gmail.com>

gcc/ChangeLog
	PR target/103611
	* config/i386/i386.md (any_or_plus): New code iterator.
	(define_split): Split (HI<<32)|zext(LO) into piece-wise
	move instructions on !TARGET_64BIT.
	* config/i386/sse.md (*vec_extractv4si_0_zext_sse4):
	Restrict to TARGET_64BIT.

gcc/testsuite/ChangeLog
	PR target/103611
	* gcc.target/i386/pr103611-2.c: New test case.

diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index 862d933..d25453f 100644 (file)
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -10644,6 +10644,38 @@
   [(set_attr "isa" "*,nox64")
    (set_attr "type" "alu")
    (set_attr "mode" "QI")])
+
+;; Split DST = (HI<<32)|LO early to minimize register usage.
+(define_code_iterator any_or_plus [plus ior xor])
+(define_split
+  [(set (match_operand:DI 0 "register_operand")
+       (any_or_plus:DI
+         (ashift:DI (match_operand:DI 1 "register_operand")
+                    (const_int 32))
+         (zero_extend:DI (match_operand:SI 2 "register_operand"))))]
+  "!TARGET_64BIT"
+  [(set (match_dup 3) (match_dup 4))
+   (set (match_dup 5) (match_dup 2))]
+{
+  operands[3] = gen_highpart (SImode, operands[0]);
+  operands[4] = gen_lowpart (SImode, operands[1]);
+  operands[5] = gen_lowpart (SImode, operands[0]);
+})
+
+(define_split
+  [(set (match_operand:DI 0 "register_operand")
+       (any_or_plus:DI
+         (zero_extend:DI (match_operand:SI 1 "register_operand"))
+         (ashift:DI (match_operand:DI 2 "register_operand")
+                    (const_int 32))))]
+  "!TARGET_64BIT"
+  [(set (match_dup 3) (match_dup 4))
+   (set (match_dup 5) (match_dup 1))]
+{
+  operands[3] = gen_highpart (SImode, operands[0]);
+  operands[4] = gen_lowpart (SImode, operands[2]);
+  operands[5] = gen_lowpart (SImode, operands[0]);
+})
 \f
 ;; Negation instructions
 

diff --git a/gcc/config/i386/sse.md b/gcc/config/i386/sse.md
index 97ce5b3..827ffbb 100644 (file)
--- a/gcc/config/i386/sse.md
+++ b/gcc/config/i386/sse.md
@@ -18747,9 +18747,9 @@
          (vec_select:SI
            (match_operand:V4SI 1 "register_operand" "v,x,v")
            (parallel [(const_int 0)]))))]
-  "TARGET_SSE4_1"
+  "TARGET_64BIT && TARGET_SSE4_1"
   "#"
-  [(set_attr "isa" "x64,*,avx512f")
+  [(set_attr "isa" "*,*,avx512f")
    (set (attr "preferred_for_speed")
      (cond [(eq_attr "alternative" "0")
              (symbol_ref "TARGET_INTER_UNIT_MOVES_FROM_VEC")

diff --git a/gcc/testsuite/gcc.target/i386/pr103611-2.c b/gcc/testsuite/gcc.target/i386/pr103611-2.c
new file mode 100644 (file)
index 0000000..1555e99
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr103611-2.c
@@ -0,0 +1,43 @@
+/* { dg-do compile } */
+/* { dg-options "-m32 -O2 -msse4" } */
+typedef int __v4si __attribute__ ((__vector_size__ (16)));
+
+long long test1(__v4si v) {
+  unsigned int loVal = (unsigned int)v[0];
+  unsigned int hiVal = (unsigned int)v[1];
+  return (long long)(loVal) | ((long long)(hiVal) << 32);
+}
+
+long long test2(__v4si v) {
+  unsigned int loVal = (unsigned int)v[2];
+  unsigned int hiVal = (unsigned int)v[3];
+  return (long long)(loVal) | ((long long)(hiVal) << 32);
+}
+
+long long test3(__v4si v) {
+  unsigned int loVal = (unsigned int)v[0];
+  unsigned int hiVal = (unsigned int)v[1];
+  return (long long)(loVal) ^ ((long long)(hiVal) << 32);
+}
+
+long long test4(__v4si v) {
+  unsigned int loVal = (unsigned int)v[2];
+  unsigned int hiVal = (unsigned int)v[3];
+  return (long long)(loVal) ^ ((long long)(hiVal) << 32);
+}
+
+long long test5(__v4si v) {
+  unsigned int loVal = (unsigned int)v[0];
+  unsigned int hiVal = (unsigned int)v[1];
+  return (long long)(loVal) + ((long long)(hiVal) << 32);
+}
+
+long long test6(__v4si v) {
+  unsigned int loVal = (unsigned int)v[2];
+  unsigned int hiVal = (unsigned int)v[3];
+  return (long long)(loVal) + ((long long)(hiVal) << 32);
+}
+
+/* { dg-final { scan-assembler-not "\tor" } } */
+/* { dg-final { scan-assembler-not "\txor" } } */
+/* { dg-final { scan-assembler-not "\tadd" } } */