diff mbox series

[committed] i386: Use SHR to compare with large power-of-two constants [PR94650]

Message ID CAFULd4Zft6A7qT+POBR-FuLLwxuUa8pEroiGK2kUQwy5acdVUQ@mail.gmail.com
State New
Headers show
Series [committed] i386: Use SHR to compare with large power-of-two constants [PR94650] | expand

Commit Message

Uros Bizjak May 4, 2020, 11:53 a.m. UTC
Convert unsigned compares where

    m >= LARGE_POWER_OF_TWO

and LARGE_POWER_OF_TWO represent an immediate where bit 33+ is set to use
a SHR instruction and compare the result to 0.  This avoids loading a
large immediate with MOVABS insn.

        movabsq $1099511627775, %rax
        cmpq    %rax, %rdi
        ja      .L5

gets converted to:

    shrq    $40, %rdi
    jne    .L5

2020-05-04  UroŇ° Bizjak  <ubizjak@gmail.com>

    PR target/94650
    * config/i386/predicates.md (shr_comparison_operator): New predicate.
    * config/i386/i386.md (compare->shr splitter): New splitters.

testsuite/ChangeLog:

2020-05-04  UroŇ° Bizjak  <ubizjak@gmail.com>

    PR target/94650
    * gcc.targeti/i386/pr94650.c: New test.

Bootstrapped and regression tested on x86_64-linux-gnu {,-m32}.

Committed to mainline SVN.

Uros.
diff mbox series

Patch

diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index 6f3ac3ad555..bd144ab3d5e 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -12310,6 +12310,36 @@ 
 
 ;; Store-flag instructions.
 
+(define_split
+  [(set (match_operand:QI 0 "nonimmediate_operand")
+	(match_operator:QI 1 "shr_comparison_operator"
+	  [(match_operand:DI 2 "register_operand")
+	   (match_operand 3 "const_int_operand")]))]
+  "TARGET_64BIT
+   && IN_RANGE (exact_log2 (UINTVAL (operands[3]) + 1), 32, 63)"
+  [(parallel
+     [(set (reg:CCZ FLAGS_REG)
+	   (compare:CCZ
+	     (lshiftrt:DI (match_dup 2) (match_dup 4))
+	     (const_int 0)))
+      (clobber (scratch:DI))])
+   (set (match_dup 0)
+	(match_op_dup 1 [(reg:CCZ FLAGS_REG) (const_int 0)]))]
+{
+  enum rtx_code new_code;
+
+  operands[1] = shallow_copy_rtx (operands[1]);
+  switch (GET_CODE (operands[1]))
+    {
+    case GTU: new_code = NE; break;
+    case LEU: new_code = EQ; break;
+    default: gcc_unreachable ();
+    }
+  PUT_CODE (operands[1], new_code);
+
+  operands[4] = GEN_INT (exact_log2 (UINTVAL (operands[3]) + 1));
+})
+
 ;; For all sCOND expanders, also expand the compare or test insn that
 ;; generates cc0.  Generate an equality comparison if `seq' or `sne'.
 
@@ -12473,6 +12503,42 @@ 
    (set_attr "mode" "<MODE>")])
 
 ;; Basic conditional jump instructions.
+
+(define_split
+  [(set (pc)
+	(if_then_else
+	  (match_operator 1 "shr_comparison_operator"
+	    [(match_operand:DI 2 "register_operand")
+	     (match_operand 3 "const_int_operand")])
+	  (label_ref (match_operand 0))
+	  (pc)))]
+  "TARGET_64BIT
+   && IN_RANGE (exact_log2 (UINTVAL (operands[3]) + 1), 32, 63)"
+  [(parallel
+     [(set (reg:CCZ FLAGS_REG)
+	   (compare:CCZ
+	     (lshiftrt:DI (match_dup 2) (match_dup 4))
+	     (const_int 0)))
+      (clobber (scratch:DI))])
+   (set (pc)
+	(if_then_else (match_op_dup 1 [(reg:CCZ FLAGS_REG) (const_int 0)])
+		      (label_ref (match_operand 0))
+		      (pc)))]
+{
+  enum rtx_code new_code;
+
+  operands[1] = shallow_copy_rtx (operands[1]);
+  switch (GET_CODE (operands[1]))
+    {
+    case GTU: new_code = NE; break;
+    case LEU: new_code = EQ; break;
+    default: gcc_unreachable ();
+    }
+  PUT_CODE (operands[1], new_code);
+
+  operands[4] = GEN_INT (exact_log2 (UINTVAL (operands[3]) + 1));
+})
+
 ;; We ignore the overflow flag for signed branch instructions.
 
 (define_insn "*jcc"
diff --git a/gcc/config/i386/predicates.md b/gcc/config/i386/predicates.md
index 71f4cb1193c..1a5e2210eca 100644
--- a/gcc/config/i386/predicates.md
+++ b/gcc/config/i386/predicates.md
@@ -1290,6 +1290,9 @@ 
 (define_predicate "bt_comparison_operator"
   (match_code "ne,eq"))
 
+(define_predicate "shr_comparison_operator"
+  (match_code "gtu,leu"))
+
 ;; Return true if OP is a valid comparison operator in valid mode.
 (define_predicate "ix86_comparison_operator"
   (match_operand 0 "comparison_operator")
diff --git a/gcc/testsuite/gcc.target/i386/pr94650.c b/gcc/testsuite/gcc.target/i386/pr94650.c
new file mode 100644
index 00000000000..49d8b6e7f8c
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr94650.c
@@ -0,0 +1,30 @@ 
+/* PR target/94650 */
+/* { dg-do compile { target { ! ia32 } } } */
+/* { dg-options "-O2" } */
+
+#define LARGE_POWER_OF_TWO (1ULL << 40)
+
+int
+check (unsigned long long m)
+{
+  return m >= LARGE_POWER_OF_TWO;
+}
+
+void g (int);
+
+void
+test0 (unsigned long long m)
+{
+  if (m >= LARGE_POWER_OF_TWO)
+    g (0);
+}
+
+void
+test1 (unsigned long long m)
+{
+  if (m >= LARGE_POWER_OF_TWO)
+    g (m);
+}
+
+/* { dg-final { scan-assembler-not "movabs" } } */
+/* { dg-final { scan-assembler-times "shr" 3 } } */