The compiler is able to merge LTU comparisons with PLUS or MINUS pattern to
form addition with carry (ADC) and subtraction with borrow (SBB) instructions:
op = op + carry [ADC $0, op]
op = op - carry [SBB $0, op]
The patch introduces reversed ADC and SBB insn patterns:
op = op + !carry [SBB $-1, op]
op = op - !carry [ADC $-1, op]
allowing the compiler to also merge GEU comparisons.
2021-04-30 Uroš Bizjak <ubiz...@gmail.com>
gcc/
PR target/98060
* config/i386/i386.md (*add<mode>3_carry_0r): New insn pattern.
(*addsi3_carry_zext_0r): Ditto.
(*sub<mode>3_carry_0): Ditto.
(*subsi3_carry_zext_0r): Ditto.
* config/i386/predicates.md (ix86_carry_flag_unset_operator):
New predicate.
* config/i386/i386.c (ix86_rtx_costs) <case PLUS, case MINUS>:
Also consider ix86_carry_flag_unset_operator to calculate
the cost of adc/sbb insn.
gcc/testsuite/
PR target/98060
* gcc.target/i386/pr98060.c: New test.
Bootstrapped and regression tested on x86_64-linux-gnu {,-m32}.
Pushed to master.
Uros.
diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index 68f33f96f5a..2f896efb5e2 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -20057,13 +20057,16 @@ ix86_rtx_costs (rtx x, machine_mode mode, int
outer_code_i, int opno,
}
else if (GET_CODE (XEXP (x, 0)) == PLUS)
{
+ rtx op = XEXP (XEXP (x, 0), 0);
+
/* Add with carry, ignore the cost of adding a carry flag. */
- if (ix86_carry_flag_operator (XEXP (XEXP (x, 0), 0), mode))
+ if (ix86_carry_flag_operator (op, mode)
+ || ix86_carry_flag_unset_operator (op, mode))
*total = cost->add;
else
{
*total = cost->lea;
- *total += rtx_cost (XEXP (XEXP (x, 0), 0), mode,
+ *total += rtx_cost (op, mode,
outer_code, opno, speed);
}
@@ -20081,7 +20084,8 @@ ix86_rtx_costs (rtx x, machine_mode mode, int
outer_code_i, int opno,
if (GET_MODE_CLASS (mode) == MODE_INT
&& GET_MODE_SIZE (mode) <= UNITS_PER_WORD
&& GET_CODE (XEXP (x, 0)) == MINUS
- && ix86_carry_flag_operator (XEXP (XEXP (x, 0), 1), mode))
+ && (ix86_carry_flag_operator (XEXP (XEXP (x, 0), 1), mode)
+ || ix86_carry_flag_unset_operator (XEXP (XEXP (x, 0), 1), mode)))
{
*total = cost->add;
*total += rtx_cost (XEXP (XEXP (x, 0), 0), mode,
diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index b7f3e36a70c..bb89eb97c69 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -6773,8 +6773,8 @@ (define_insn "@add<mode>3_carry"
(define_insn "*add<mode>3_carry_0"
[(set (match_operand:SWI 0 "nonimmediate_operand" "=<r>m")
(plus:SWI
- (match_operator:SWI 3 "ix86_carry_flag_operator"
- [(match_operand 2 "flags_reg_operand") (const_int 0)])
+ (match_operator:SWI 2 "ix86_carry_flag_operator"
+ [(reg FLAGS_REG) (const_int 0)])
(match_operand:SWI 1 "nonimmediate_operand" "0")))
(clobber (reg:CC FLAGS_REG))]
"!MEM_P (operands[0]) || rtx_equal_p (operands[0], operands[1])"
@@ -6784,6 +6784,20 @@ (define_insn "*add<mode>3_carry_0"
(set_attr "pent_pair" "pu")
(set_attr "mode" "<MODE>")])
+(define_insn "*add<mode>3_carry_0r"
+ [(set (match_operand:SWI 0 "nonimmediate_operand" "=<r>m")
+ (plus:SWI
+ (match_operator:SWI 2 "ix86_carry_flag_unset_operator"
+ [(reg FLAGS_REG) (const_int 0)])
+ (match_operand:SWI 1 "nonimmediate_operand" "0")))
+ (clobber (reg:CC FLAGS_REG))]
+ "!MEM_P (operands[0]) || rtx_equal_p (operands[0], operands[1])"
+ "sbb{<imodesuffix>}\t{$-1, %0|%0, -1}"
+ [(set_attr "type" "alu")
+ (set_attr "use_carry" "1")
+ (set_attr "pent_pair" "pu")
+ (set_attr "mode" "<MODE>")])
+
(define_insn "*addsi3_carry_zext"
[(set (match_operand:DI 0 "register_operand" "=r")
(zero_extend:DI
@@ -6814,6 +6828,20 @@ (define_insn "*addsi3_carry_zext_0"
(set_attr "pent_pair" "pu")
(set_attr "mode" "SI")])
+(define_insn "*addsi3_carry_zext_0r"
+ [(set (match_operand:DI 0 "register_operand" "=r")
+ (zero_extend:DI
+ (plus:SI (match_operator:SI 2 "ix86_carry_flag_unset_operator"
+ [(reg FLAGS_REG) (const_int 0)])
+ (match_operand:SI 1 "register_operand" "0"))))
+ (clobber (reg:CC FLAGS_REG))]
+ "TARGET_64BIT"
+ "sbb{l}\t{$-1, %k0|%k0, -1}"
+ [(set_attr "type" "alu")
+ (set_attr "use_carry" "1")
+ (set_attr "pent_pair" "pu")
+ (set_attr "mode" "SI")])
+
;; There is no point to generate ADCX instruction. ADC is shorter and faster.
(define_insn "addcarry<mode>"
@@ -6916,8 +6944,8 @@ (define_insn "*sub<mode>3_carry_0"
[(set (match_operand:SWI 0 "nonimmediate_operand" "=<r>m")
(minus:SWI
(match_operand:SWI 1 "nonimmediate_operand" "0")
- (match_operator:SWI 3 "ix86_carry_flag_operator"
- [(match_operand 2 "flags_reg_operand") (const_int 0)])))
+ (match_operator:SWI 2 "ix86_carry_flag_operator"
+ [(reg FLAGS_REG) (const_int 0)])))
(clobber (reg:CC FLAGS_REG))]
"!MEM_P (operands[0]) || rtx_equal_p (operands[0], operands[1])"
"sbb{<imodesuffix>}\t{$0, %0|%0, 0}"
@@ -6926,6 +6954,20 @@ (define_insn "*sub<mode>3_carry_0"
(set_attr "pent_pair" "pu")
(set_attr "mode" "<MODE>")])
+(define_insn "*sub<mode>3_carry_0r"
+ [(set (match_operand:SWI 0 "nonimmediate_operand" "=<r>m")
+ (minus:SWI
+ (match_operand:SWI 1 "nonimmediate_operand" "0")
+ (match_operator:SWI 2 "ix86_carry_flag_unset_operator"
+ [(reg FLAGS_REG) (const_int 0)])))
+ (clobber (reg:CC FLAGS_REG))]
+ "!MEM_P (operands[0]) || rtx_equal_p (operands[0], operands[1])"
+ "adc{<imodesuffix>}\t{$-1, %0|%0, -1}"
+ [(set_attr "type" "alu")
+ (set_attr "use_carry" "1")
+ (set_attr "pent_pair" "pu")
+ (set_attr "mode" "<MODE>")])
+
(define_insn "*subsi3_carry_zext"
[(set (match_operand:DI 0 "register_operand" "=r")
(zero_extend:DI
@@ -6958,6 +7000,21 @@ (define_insn "*subsi3_carry_zext_0"
(set_attr "pent_pair" "pu")
(set_attr "mode" "SI")])
+(define_insn "*subsi3_carry_zext_0r"
+ [(set (match_operand:DI 0 "register_operand" "=r")
+ (zero_extend:DI
+ (minus:SI
+ (match_operand:SI 1 "register_operand" "0")
+ (match_operator:SI 2 "ix86_carry_flag_unset_operator"
+ [(reg FLAGS_REG) (const_int 0)]))))
+ (clobber (reg:CC FLAGS_REG))]
+ "TARGET_64BIT"
+ "adc{l}\t{$-1, %k0|%k0, -1}"
+ [(set_attr "type" "alu")
+ (set_attr "use_carry" "1")
+ (set_attr "pent_pair" "pu")
+ (set_attr "mode" "SI")])
+
(define_insn "@sub<mode>3_carry_ccc"
[(set (reg:CCC FLAGS_REG)
(compare:CCC
diff --git a/gcc/config/i386/predicates.md b/gcc/config/i386/predicates.md
index 04a03a70b46..6dfbb0873be 100644
--- a/gcc/config/i386/predicates.md
+++ b/gcc/config/i386/predicates.md
@@ -1455,6 +1455,22 @@ (define_predicate "ix86_carry_flag_operator"
return code == LTU;
})
+;; Return true if OP is a valid comparison operator
+;; testing carry flag to be unset.
+(define_predicate "ix86_carry_flag_unset_operator"
+ (match_code "geu,ge")
+{
+ machine_mode inmode = GET_MODE (XEXP (op, 0));
+ enum rtx_code code = GET_CODE (op);
+
+ if (inmode == CCFPmode)
+ code = ix86_fp_compare_code_to_integer (code);
+ else if (inmode != CCmode && inmode != CCCmode && inmode != CCGZmode)
+ return false;
+
+ return code == GEU;
+})
+
;; Return true if this comparison only requires testing one flag bit.
(define_predicate "ix86_trivial_fp_comparison_operator"
(match_code "gt,ge,unlt,unle,uneq,ltgt,ordered,unordered"))
diff --git a/gcc/testsuite/gcc.target/i386/pr98060.c
b/gcc/testsuite/gcc.target/i386/pr98060.c
new file mode 100644
index 00000000000..f82620ceb64
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr98060.c
@@ -0,0 +1,47 @@
+/* PR target/98060 */
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+/* { dg-final { scan-assembler-not "set" } } */
+/* { dg-final { scan-assembler-times "adc" 4 } } */
+/* { dg-final { scan-assembler-times "sbb" 4 } } */
+
+int r1 (unsigned v0, unsigned v1, int v2)
+{
+ return v2 + (v0 >= v1);
+}
+
+int r2 (unsigned v0, unsigned v1, int v2)
+{
+ return v2 + (v0 <= v1);
+}
+
+int r3 (unsigned v0, unsigned v1, int v2)
+{
+ return v2 + (v0 > v1);
+}
+
+int r4 (unsigned v0, unsigned v1, int v2)
+{
+ return v2 + (v0 < v1);
+}
+
+int r5 (unsigned v0, unsigned v1, int v2)
+{
+ return v2 - (v0 >= v1);
+}
+
+int r6 (unsigned v0, unsigned v1, int v2)
+{
+ return v2 - (v0 <= v1);
+}
+
+int r7 (unsigned v0, unsigned v1, int v2)
+{
+ return v2 - (v0 > v1);
+}
+
+int r8 (unsigned v0, unsigned v1, int v2)
+{
+ return v2 - (v0 < v1);
+}
