This patch teaches the i386 backend to avoid using BMI2's rorx
instructions when optimizing for size. The benefits are shown
with the following example:
unsigned int ror1(unsigned int x) { return (x >> 1) | (x << 31); }
unsigned int ror2(unsigned int x) { return (x >> 2) | (x << 30); }
unsigned int rol2(unsigned int x) { return (x >> 30) | (x << 2); }
unsigned int rol1(unsigned int x) { return (x >> 31) | (x << 1); }
which currently with -Os -march=cascadelake generates:
ror1: rorx $1, %edi, %eax // 6 bytes
ret
ror2: rorx $2, %edi, %eax // 6 bytes
ret
rol2: rorx $30, %edi, %eax // 6 bytes
ret
rol1: rorx $31, %edi, %eax // 6 bytes
ret
but with this patch now generates:
ror1: movl %edi, %eax // 2 bytes
rorl %eax // 2 bytes
ret
ror2: movl %edi, %eax // 2 bytes
rorl $2, %eax // 3 bytes
ret
rol2: movl %edi, %eax // 2 bytes
roll $2, %eax // 3 bytes
ret
rol1: movl %edi, %eax // 2 bytes
roll %eax // 2 bytes
ret
I've confirmed that this patch is a win on the CSiBE benchmark,
even though rotations are rare, where for example libmspack/test/md5.o
shrinks from 5824 bytes to 5632 bytes.
This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
and make -k check with no new failures. Ok for mainline?
2021-11-15 Roger Sayle <ro...@nextmovesoftware.com>
gcc/ChangeLog
* config/i386/i386.md (*bmi2_rorx<mode3>_1): Make conditional
on !optimize_function_for_size_p.
(*<any_rotate><mode>3_1): Add preferred_for_size attribute.
(define_splits): Conditionalize on !optimize_function_for_size_p.
(*bmi2_rorxsi3_1_zext): Likewise.
(*<any_rotate>si2_1_zext): Add preferred_for_size attribute.
(define_splits): Conditionalize on !optimize_function_for_size_p.
Thanks in advance,
Roger
--
diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index 6eb9de8..7394906 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -12775,7 +12775,7 @@
(rotatert:SWI48
(match_operand:SWI48 1 "nonimmediate_operand" "rm")
(match_operand:QI 2 "<rorx_immediate_operand>" "<S>")))]
- "TARGET_BMI2"
+ "TARGET_BMI2 && !optimize_function_for_size_p (cfun)"
"rorx\t{%2, %1, %0|%0, %1, %2}"
[(set_attr "type" "rotatex")
(set_attr "mode" "<MODE>")])
@@ -12803,6 +12803,10 @@
}
[(set_attr "isa" "*,bmi2")
(set_attr "type" "rotate,rotatex")
+ (set (attr "preferred_for_size")
+ (cond [(eq_attr "alternative" "0")
+ (symbol_ref "true")]
+ (symbol_ref "false")))
(set (attr "length_immediate")
(if_then_else
(and (eq_attr "type" "rotate")
@@ -12819,7 +12823,7 @@
(rotate:SWI48 (match_operand:SWI48 1 "nonimmediate_operand")
(match_operand:QI 2 "const_int_operand")))
(clobber (reg:CC FLAGS_REG))]
- "TARGET_BMI2 && reload_completed"
+ "TARGET_BMI2 && reload_completed && !optimize_function_for_size_p (cfun)"
[(set (match_dup 0)
(rotatert:SWI48 (match_dup 1) (match_dup 2)))]
{
@@ -12833,7 +12837,7 @@
(rotatert:SWI48 (match_operand:SWI48 1 "nonimmediate_operand")
(match_operand:QI 2 "const_int_operand")))
(clobber (reg:CC FLAGS_REG))]
- "TARGET_BMI2 && reload_completed"
+ "TARGET_BMI2 && reload_completed && !optimize_function_for_size_p (cfun)"
[(set (match_dup 0)
(rotatert:SWI48 (match_dup 1) (match_dup 2)))])
@@ -12842,7 +12846,7 @@
(zero_extend:DI
(rotatert:SI (match_operand:SI 1 "nonimmediate_operand" "rm")
(match_operand:QI 2 "const_0_to_31_operand" "I"))))]
- "TARGET_64BIT && TARGET_BMI2"
+ "TARGET_64BIT && TARGET_BMI2 && !optimize_function_for_size_p (cfun)"
"rorx\t{%2, %1, %k0|%k0, %1, %2}"
[(set_attr "type" "rotatex")
(set_attr "mode" "SI")])
@@ -12870,6 +12874,10 @@
}
[(set_attr "isa" "*,bmi2")
(set_attr "type" "rotate,rotatex")
+ (set (attr "preferred_for_size")
+ (cond [(eq_attr "alternative" "0")
+ (symbol_ref "true")]
+ (symbol_ref "false")))
(set (attr "length_immediate")
(if_then_else
(and (eq_attr "type" "rotate")
@@ -12887,7 +12895,8 @@
(rotate:SI (match_operand:SI 1 "nonimmediate_operand")
(match_operand:QI 2 "const_int_operand"))))
(clobber (reg:CC FLAGS_REG))]
- "TARGET_64BIT && TARGET_BMI2 && reload_completed"
+ "TARGET_64BIT && TARGET_BMI2 && reload_completed
+ && !optimize_function_for_size_p (cfun)"
[(set (match_dup 0)
(zero_extend:DI (rotatert:SI (match_dup 1) (match_dup 2))))]
{
@@ -12902,7 +12911,8 @@
(rotatert:SI (match_operand:SI 1 "nonimmediate_operand")
(match_operand:QI 2 "const_int_operand"))))
(clobber (reg:CC FLAGS_REG))]
- "TARGET_64BIT && TARGET_BMI2 && reload_completed"
+ "TARGET_64BIT && TARGET_BMI2 && reload_completed
+ && !optimize_function_for_size_p (cfun)"
[(set (match_dup 0)
(zero_extend:DI (rotatert:SI (match_dup 1) (match_dup 2))))])
