Add post-reload splitter for extendditi2 on x86_64.

This is another step towards a possible solution for PR 105137.
This patch introduces a define_insn for extendditi2 that allows
DImode to TImode sign-extension to be represented in the early
RTL optimizers, before being split post-reload into the exact
same idiom as currently produced by RTL expansion.

Typically this produces the identical code, so the first new
test case:
__int128 foo(long long x) { return (__int128)x; }

continues to generate:
foo:	movq    %rdi, %rax
        cqto
        ret

The "magic" is that this representation allows combine and the
other RTL optimizers to do a better job.  Hence, the second
test case:

__int128 foo(__int128 a, long long b) {
    a += ((__int128)b) << 70;
    return a;
}

which mainline with -O2 currently generates as:

foo:	movq    %rsi, %rax
        movq    %rdx, %rcx
        movq    %rdi, %rsi
        salq    $6, %rcx
        movq    %rax, %rdi
        xorl    %eax, %eax
        movq    %rcx, %rdx
        addq    %rsi, %rax
        adcq    %rdi, %rdx
        ret

with this patch now becomes:
foo:    movl    $0, %eax
        salq    $6, %rdx
        addq    %rdi, %rax
        adcq    %rsi, %rdx
        ret

i.e. the same code for the signed and unsigned extension variants.

2023-01-01  Roger Sayle  <roger@nextmovesoftware.com>
	    Uroš Bizjak  <ubizjak@gmail.com>

gcc/ChangeLog
	* config/i386/i386.md (extendditi2): New define_insn.
	(define_split): Use DWIH mode iterator to treat new extendditi2
	identically to existing extendsidi2_1.
	(define_peephole2): Likewise.
	(define_peephole2): Likewise.
	(define_Split): Likewise.

gcc/testsuite/ChangeLog
	* gcc.target/i386/extendditi2-1.c: New test case.
	* gcc.target/i386/extendditi2-2.c: Likewise.

diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index ca40c4f..890c4c8 100644 (file)
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -4548,17 +4548,27 @@
   "!TARGET_64BIT"
   "#")
 
+(define_insn "extendditi2"
+  [(set (match_operand:TI 0 "nonimmediate_operand" "=*A,r,?r,?*o")
+       (sign_extend:TI (match_operand:DI 1 "register_operand" "0,0,r,r")))
+   (clobber (reg:CC FLAGS_REG))
+   (clobber (match_scratch:DI 2 "=X,X,X,&r"))]
+  "TARGET_64BIT"
+  "#")
+
 ;; Split the memory case.  If the source register doesn't die, it will stay
 ;; this way, if it does die, following peephole2s take care of it.
 (define_split
-  [(set (match_operand:DI 0 "memory_operand")
-       (sign_extend:DI (match_operand:SI 1 "register_operand")))
+  [(set (match_operand:<DWI> 0 "memory_operand")
+       (sign_extend:<DWI> (match_operand:DWIH 1 "register_operand")))
    (clobber (reg:CC FLAGS_REG))
-   (clobber (match_operand:SI 2 "register_operand"))]
+   (clobber (match_operand:DWIH 2 "register_operand"))]
   "reload_completed"
   [(const_int 0)]
 {
-  split_double_mode (DImode, &operands[0], 1, &operands[3], &operands[4]);
+  rtx bits = GEN_INT (<MODE_SIZE> * BITS_PER_UNIT - 1);
+
+  split_double_mode (<DWI>mode, &operands[0], 1, &operands[3], &operands[4]);
 
   emit_move_insn (operands[3], operands[1]);
 
@@ -4567,12 +4577,12 @@
       && REGNO (operands[1]) == AX_REG
       && REGNO (operands[2]) == DX_REG)
     {
-      emit_insn (gen_ashrsi3_cvt (operands[2], operands[1], GEN_INT (31)));
+      emit_insn (gen_ashr<mode>3_cvt (operands[2], operands[1], bits));
     }
   else
     {
       emit_move_insn (operands[2], operands[1]);
-      emit_insn (gen_ashrsi3_cvt (operands[2], operands[2], GEN_INT (31)));
+      emit_insn (gen_ashr<mode>3_cvt (operands[2], operands[2], bits));
     }
   emit_move_insn (operands[4], operands[2]);
   DONE;
@@ -4581,69 +4591,79 @@
 ;; Peepholes for the case where the source register does die, after
 ;; being split with the above splitter.
 (define_peephole2
-  [(set (match_operand:SI 0 "memory_operand")
-       (match_operand:SI 1 "general_reg_operand"))
-   (set (match_operand:SI 2 "general_reg_operand") (match_dup 1))
+  [(set (match_operand:DWIH 0 "memory_operand")
+       (match_operand:DWIH 1 "general_reg_operand"))
+   (set (match_operand:DWIH 2 "general_reg_operand") (match_dup 1))
    (parallel [(set (match_dup 2)
-                  (ashiftrt:SI (match_dup 2) (const_int 31)))
+                  (ashiftrt:DWIH (match_dup 2)
+                                 (match_operand 4 "const_int_operand")))
               (clobber (reg:CC FLAGS_REG))])
-   (set (match_operand:SI 3 "memory_operand") (match_dup 2))]
+   (set (match_operand:DWIH 3 "memory_operand") (match_dup 2))]
   "REGNO (operands[1]) != REGNO (operands[2])
+   && INTVAL (operands[4]) == (<MODE_SIZE> * BITS_PER_UNIT - 1)
    && peep2_reg_dead_p (2, operands[1])
    && peep2_reg_dead_p (4, operands[2])
    && !reg_mentioned_p (operands[2], operands[3])"
   [(set (match_dup 0) (match_dup 1))
-   (parallel [(set (match_dup 1) (ashiftrt:SI (match_dup 1) (const_int 31)))
+   (parallel [(set (match_dup 1) (ashiftrt:DWIH (match_dup 1) (match_dup 4)))
              (clobber (reg:CC FLAGS_REG))])
    (set (match_dup 3) (match_dup 1))])
 
 (define_peephole2
-  [(set (match_operand:SI 0 "memory_operand")
-       (match_operand:SI 1 "general_reg_operand"))
-   (parallel [(set (match_operand:SI 2 "general_reg_operand")
-                  (ashiftrt:SI (match_dup 1) (const_int 31)))
+  [(set (match_operand:DWIH 0 "memory_operand")
+       (match_operand:DWIH 1 "general_reg_operand"))
+   (parallel [(set (match_operand:DWIH 2 "general_reg_operand")
+                  (ashiftrt:DWIH (match_dup 1)
+                                 (match_operand 4 "const_int_operand")))
               (clobber (reg:CC FLAGS_REG))])
-   (set (match_operand:SI 3 "memory_operand") (match_dup 2))]
+   (set (match_operand:DWIH 3 "memory_operand") (match_dup 2))]
   "/* cltd is shorter than sarl $31, %eax */
    !optimize_function_for_size_p (cfun)
    && REGNO (operands[1]) == AX_REG
    && REGNO (operands[2]) == DX_REG
+   && INTVAL (operands[4]) == (<MODE_SIZE> * BITS_PER_UNIT - 1)
    && peep2_reg_dead_p (2, operands[1])
    && peep2_reg_dead_p (3, operands[2])
    && !reg_mentioned_p (operands[2], operands[3])"
   [(set (match_dup 0) (match_dup 1))
-   (parallel [(set (match_dup 1) (ashiftrt:SI (match_dup 1) (const_int 31)))
+   (parallel [(set (match_dup 1) (ashiftrt:DWIH (match_dup 1) (match_dup 4)))
              (clobber (reg:CC FLAGS_REG))])
    (set (match_dup 3) (match_dup 1))])
 
 ;; Extend to register case.  Optimize case where source and destination
 ;; registers match and cases where we can use cltd.
 (define_split
-  [(set (match_operand:DI 0 "register_operand")
-       (sign_extend:DI (match_operand:SI 1 "register_operand")))
+  [(set (match_operand:<DWI> 0 "register_operand")
+       (sign_extend:<DWI> (match_operand:DWIH 1 "register_operand")))
    (clobber (reg:CC FLAGS_REG))
-   (clobber (match_scratch:SI 2))]
+   (clobber (match_scratch:DWIH 2))]
   "reload_completed"
   [(const_int 0)]
 {
-  split_double_mode (DImode, &operands[0], 1, &operands[3], &operands[4]);
+  rtx bits = GEN_INT (<MODE_SIZE> * BITS_PER_UNIT - 1);
+
+  split_double_mode (<DWI>mode, &operands[0], 1, &operands[3], &operands[4]);
 
   if (REGNO (operands[3]) != REGNO (operands[1]))
     emit_move_insn (operands[3], operands[1]);
 
+  rtx src = operands[1];
+  if (REGNO (operands[3]) == AX_REG)
+    src = operands[3];
+
   /* Generate a cltd if possible and doing so it profitable.  */
   if ((optimize_function_for_size_p (cfun) || TARGET_USE_CLTD)
-      && REGNO (operands[3]) == AX_REG
+      && REGNO (src) == AX_REG
       && REGNO (operands[4]) == DX_REG)
     {
-      emit_insn (gen_ashrsi3_cvt (operands[4], operands[3], GEN_INT (31)));
+      emit_insn (gen_ashr<mode>3_cvt (operands[4], src, bits));
       DONE;
     }
 
   if (REGNO (operands[4]) != REGNO (operands[1]))
     emit_move_insn (operands[4], operands[1]);
 
-  emit_insn (gen_ashrsi3_cvt (operands[4], operands[4], GEN_INT (31)));
+  emit_insn (gen_ashr<mode>3_cvt (operands[4], operands[4], bits));
   DONE;
 })
 

diff --git a/gcc/testsuite/gcc.target/i386/extendditi2-1.c b/gcc/testsuite/gcc.target/i386/extendditi2-1.c
new file mode 100644 (file)
index 0000000..efbad0e
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/extendditi2-1.c
@@ -0,0 +1,8 @@
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-O2" } */
+
+__int128 foo(long long x)
+{
+  return (__int128)x;
+}
+/* { dg-final { scan-assembler "cqt?o" } } */

diff --git a/gcc/testsuite/gcc.target/i386/extendditi2-2.c b/gcc/testsuite/gcc.target/i386/extendditi2-2.c
new file mode 100644 (file)
index 0000000..dbfa6fb
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/extendditi2-2.c
@@ -0,0 +1,13 @@
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-O2" } */
+
+__int128 foo(__int128 a, long long b) {
+    a += ((__int128)b) << 70;
+    return a;
+}
+
+__int128 bar(__int128 a, unsigned long long b) {
+    a += ((__int128)b) << 70;
+    return a;
+}
+/* { dg-final { scan-assembler-not "movq" } } */