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 Uroš Bizjak <ubiz...@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 Uroš Bizjak <ubiz...@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 --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 } } */
