[gcc r13-1982] Allow any immediate constant in *cmp<dwi>_doubleword splitter on x86_64.

[gcc r13-1982] Allow any immediate constant in *cmp<dwi>_doubleword splitter on x86_64.

[Roger Sayle]

https://gcc.gnu.org/g:a46bca36b7b3a8a7e15b04225fb2b4f9b1bed62c

commit r13-1982-ga46bca36b7b3a8a7e15b04225fb2b4f9b1bed62c
Author: Roger Sayle <roger@nextmovesoftware.com>
Date:   Sun Aug 7 08:49:48 2022 +0100

    Allow any immediate constant in *cmp<dwi>_doubleword splitter on x86_64.
    
    This patch tweaks i386.md's *cmp<dwi>_doubleword splitter's predicate to
    allow general_operand, not just x86_64_hilo_general_operand, to improve
    code generation.  As a general rule, i386.md's _doubleword splitters should
    be post-reload splitters that require integer immediate operands to be
    x86_64_hilo_int_operand, so that each part is a valid word mode immediate
    constant.  As an exception to this rule, doubleword patterns that must be
    split before reload, because they require additional scratch registers,
    can use take advantage of this ability to create new pseudos, to accept
    any immediate constant, and call force_reg on the high and/or low parts
    if they are not suitable immediate operands in word mode.
    
    The benefit is shown in the new cmpti3.c test case below.
    
    __int128 x;
    int foo()
    {
        __int128 t = 0x1234567890abcdefLL;
        return x == t;
    }
    
    where GCC with -O2 currently generates:
    
            movabsq $1311768467294899695, %rax
            xorl    %edx, %edx
            xorq    x(%rip), %rax
            xorq    x+8(%rip), %rdx
            orq     %rdx, %rax
            sete    %al
            movzbl  %al, %eax
            ret
    
    but with this patch now generates:
    
            movabsq $1311768467294899695, %rax
            xorq    x(%rip), %rax
            orq     x+8(%rip), %rax
            sete    %al
            movzbl  %al, %eax
            ret
    
    2022-08-07  Roger Sayle  <roger@nextmovesoftware.com>
    
    gcc/ChangeLog
            * config/i386/i386.md (*cmp<dwi>_doubleword): Change predicate
            for x86_64_hilo_general_operand to general operand.  Call
            force_reg on parts that are not x86_64_immediate_operand.
    
    gcc/testsuite/ChangeLog
            * gcc.target/i386/cmpti1.c: New test case.
            * gcc.target/i386/cmpti2.c: Likewise.
            * gcc.target/i386/cmpti3.c: Likewise.

Diff:
---
 gcc/config/i386/i386.md                | 16 +++++++++++++---
 gcc/testsuite/gcc.target/i386/cmpti1.c |  8 ++++++++
 gcc/testsuite/gcc.target/i386/cmpti2.c | 12 ++++++++++++
 gcc/testsuite/gcc.target/i386/cmpti3.c | 13 +++++++++++++
 4 files changed, 46 insertions(+), 3 deletions(-)

diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index 298e4b30348..fd30c573c27 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -1510,7 +1510,7 @@
 (define_insn_and_split "*cmp<dwi>_doubleword"
   [(set (reg:CCZ FLAGS_REG)
 	(compare:CCZ (match_operand:<DWI> 0 "nonimmediate_operand")
-		     (match_operand:<DWI> 1 "x86_64_hilo_general_operand")))]
+		     (match_operand:<DWI> 1 "general_operand")))]
   "ix86_pre_reload_split ()"
   "#"
   "&& 1"
@@ -1544,7 +1544,12 @@
   else if (operands[0] == constm1_rtx)
     emit_insn (gen_one_cmpl<mode>2 (operands[4], operands[1]));
   else
-    emit_insn (gen_xor<mode>3 (operands[4], operands[0], operands[1]));
+    {
+      if (CONST_SCALAR_INT_P (operands[1])
+	  && !x86_64_immediate_operand (operands[1], <MODE>mode))
+	operands[1] = force_reg (<MODE>mode, operands[1]);
+      emit_insn (gen_xor<mode>3 (operands[4], operands[0], operands[1]));
+    }
 
   if (operands[3] == const0_rtx)
     operands[5] = operands[2];
@@ -1558,7 +1563,12 @@
       else if (operands[2] == constm1_rtx)
 	emit_insn (gen_one_cmpl<mode>2 (operands[5], operands[3]));
       else
-	emit_insn (gen_xor<mode>3 (operands[5], operands[2], operands[3]));
+	{
+	  if (CONST_SCALAR_INT_P (operands[3])
+	      && !x86_64_immediate_operand (operands[3], <MODE>mode))
+	    operands[3] = force_reg (<MODE>mode, operands[3]);
+	  emit_insn (gen_xor<mode>3 (operands[5], operands[2], operands[3]));
+	}
     }
 })
 
diff --git a/gcc/testsuite/gcc.target/i386/cmpti1.c b/gcc/testsuite/gcc.target/i386/cmpti1.c
new file mode 100644
index 00000000000..1c5f121e544
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/cmpti1.c
@@ -0,0 +1,8 @@
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-O2" } */
+int eq(__int128 x, __int128 y) { return x == y; }
+int ne(__int128 x, __int128 y) { return x != y; }
+/* { dg-final { scan-assembler-times "xorq" 4 } } */
+/* { dg-final { scan-assembler-times "setne" 1 } } */
+/* { dg-final { scan-assembler-times "sete" 1 } } */
+
diff --git a/gcc/testsuite/gcc.target/i386/cmpti2.c b/gcc/testsuite/gcc.target/i386/cmpti2.c
new file mode 100644
index 00000000000..ad9572901ce
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/cmpti2.c
@@ -0,0 +1,12 @@
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-O2" } */
+
+__int128 x;
+__int128 y;
+
+int eq() { return x == y; }
+int ne() { return x != y; }
+
+/* { dg-final { scan-assembler-times "xorq" 4 } } */
+/* { dg-final { scan-assembler-times "setne" 1 } } */
+/* { dg-final { scan-assembler-times "sete" 1 } } */
diff --git a/gcc/testsuite/gcc.target/i386/cmpti3.c b/gcc/testsuite/gcc.target/i386/cmpti3.c
new file mode 100644
index 00000000000..302efd2ad59
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/cmpti3.c
@@ -0,0 +1,13 @@
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-O2" } */
+
+__int128 x;
+int foo()
+{
+    __int128 t = 0x1234567890abcdefLL;
+    return x == t;
+}
+
+/* { dg-final { scan-assembler-times "movabsq" 1 } } */
+/* { dg-final { scan-assembler-times "xorq" 1 } } */
+/* { dg-final { scan-assembler-not "xorl" } } */