While working on a middle-end patch to more aggressively use highpart
multiplications on targets that support them, I noticed that the RTL
expanded by the x86 backend interacts poorly with register allocation
leading to suboptimal code.
For the testcase,
typedef int __attribute ((mode(TI))) ti_t;
long foo(long x)
{
return ((ti_t)x * 19065) >> 64;
}
we'd like to avoid:
foo: movq %rdi, %rax
movl $19065, %edx
imulq %rdx
movq %rdx, %rax
ret
and would prefer:
foo: movl $19065, %eax
imulq %rdi
movq %rdx, %rax
ret
This patch provides a pair of peephole2 transformations to tweak the
spills generated by reload, and at the same time replaces the current
define_expand with define_insn patterns using the new [su]mul_highpart
RTX codes. I've left the old-style patterns in the machine description
for the time being, but plan to remove these once my planned middle-end
improvements make them obsolete.
This patch has been tested on x86_64-pc-linux-gnu (both with and without
the middle-end changes) by make bootstrap and make -k check with no new
failures. The new test case, which currently passes, ensures that the
code we generate isn't adversely affected by changes outside the backend.
Ok for mainline?
2021-12-10 Roger Sayle <ro...@nextmovesoftware.com>
gcc/ChangeLog
* config/i386/i386.md (any_mul_highpart): New code iterator.
(sgnprefix, s): Add attribute support for [su]mul_highpart.
(<s>mul<mode>3_highpart): Delete expander.
(<s>muldi3_highpart, <s>mulsi3_highpart, <s>mulsi32_highpart_zext):
New define_insn patterns.
(define_peephole2): Tweak the register allocation for the above
instructions after reload.
gcc/testsuite/ChangeLog
* gcc.target/i386/smuldi3_highpart.c: New test case.
Thanks in advance,
Roger
--
diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index 4e9fae8..fc79146 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -992,11 +992,16 @@
;; Mapping of extend operators
(define_code_iterator any_extend [sign_extend zero_extend])
+;; Mapping of highpart multiply operators
+(define_code_iterator any_mul_highpart [smul_highpart umul_highpart])
+
;; Prefix for insn menmonic.
(define_code_attr sgnprefix [(sign_extend "i") (zero_extend "")
+ (smul_highpart "i") (umul_highpart "")
(div "i") (udiv "")])
;; Prefix for define_insn
-(define_code_attr s [(sign_extend "s") (zero_extend "u")])
+(define_code_attr s [(sign_extend "s") (zero_extend "u")
+ (smul_highpart "s") (umul_highpart "u")])
(define_code_attr u [(sign_extend "") (zero_extend "u")
(div "") (udiv "u")])
(define_code_attr u_bool [(sign_extend "false") (zero_extend "true")
@@ -8426,20 +8431,64 @@
(set_attr "bdver1_decode" "direct")
(set_attr "mode" "QI")])
-(define_expand "<s>mul<mode>3_highpart"
- [(parallel [(set (match_operand:DWIH 0 "register_operand")
- (truncate:DWIH
- (lshiftrt:<DWI>
- (mult:<DWI>
- (any_extend:<DWI>
- (match_operand:DWIH 1 "nonimmediate_operand"))
- (any_extend:<DWI>
- (match_operand:DWIH 2 "register_operand")))
- (match_dup 3))))
- (clobber (scratch:DWIH))
- (clobber (reg:CC FLAGS_REG))])]
+;; Highpart multiplication patterns
+(define_insn "<s>muldi3_highpart"
+ [(set (match_operand:DI 0 "register_operand" "=d")
+ (any_mul_highpart:DI
+ (match_operand:DI 1 "register_operand" "%a")
+ (match_operand:DI 2 "nonimmediate_operand" "rm")))
+ (clobber (match_scratch:DI 3 "=1"))
+ (clobber (reg:CC FLAGS_REG))]
+ "TARGET_64BIT"
+ "<sgnprefix>mul{q}\t%2"
+ [(set_attr "type" "imul")
+ (set_attr "length_immediate" "0")
+ (set (attr "athlon_decode")
+ (if_then_else (eq_attr "cpu" "athlon")
+ (const_string "vector")
+ (const_string "double")))
+ (set_attr "amdfam10_decode" "double")
+ (set_attr "bdver1_decode" "direct")
+ (set_attr "mode" "DI")])
+
+(define_insn "*<s>mulsi3_highpart_zext"
+ [(set (match_operand:DI 0 "register_operand" "=d")
+ (zero_extend:DI
+ (any_mul_highpart:SI
+ (match_operand:SI 1 "register_operand" "%a")
+ (match_operand:SI 2 "nonimmediate_operand" "rm"))))
+ (clobber (match_scratch:SI 3 "=1"))
+ (clobber (reg:CC FLAGS_REG))]
+ "TARGET_64BIT"
+ "<sgnprefix>mul{l}\t%2"
+ [(set_attr "type" "imul")
+ (set_attr "length_immediate" "0")
+ (set (attr "athlon_decode")
+ (if_then_else (eq_attr "cpu" "athlon")
+ (const_string "vector")
+ (const_string "double")))
+ (set_attr "amdfam10_decode" "double")
+ (set_attr "bdver1_decode" "direct")
+ (set_attr "mode" "SI")])
+
+(define_insn "*<s>mulsi3_highpart"
+ [(set (match_operand:SI 0 "register_operand" "=d")
+ (any_mul_highpart:SI
+ (match_operand:SI 1 "register_operand" "%a")
+ (match_operand:SI 2 "nonimmediate_operand" "rm")))
+ (clobber (match_scratch:SI 3 "=1"))
+ (clobber (reg:CC FLAGS_REG))]
""
- "operands[3] = GEN_INT (GET_MODE_BITSIZE (<MODE>mode));")
+ "<sgnprefix>mul{l}\t%2"
+ [(set_attr "type" "imul")
+ (set_attr "length_immediate" "0")
+ (set (attr "athlon_decode")
+ (if_then_else (eq_attr "cpu" "athlon")
+ (const_string "vector")
+ (const_string "double")))
+ (set_attr "amdfam10_decode" "double")
+ (set_attr "bdver1_decode" "direct")
+ (set_attr "mode" "SI")])
(define_insn "*<s>muldi3_highpart_1"
[(set (match_operand:DI 0 "register_operand" "=d")
@@ -8460,8 +8509,8 @@
(set_attr "length_immediate" "0")
(set (attr "athlon_decode")
(if_then_else (eq_attr "cpu" "athlon")
- (const_string "vector")
- (const_string "double")))
+ (const_string "vector")
+ (const_string "double")))
(set_attr "amdfam10_decode" "double")
(set_attr "bdver1_decode" "direct")
(set_attr "mode" "DI")])
@@ -8484,8 +8533,8 @@
(set_attr "length_immediate" "0")
(set (attr "athlon_decode")
(if_then_else (eq_attr "cpu" "athlon")
- (const_string "vector")
- (const_string "double")))
+ (const_string "vector")
+ (const_string "double")))
(set_attr "amdfam10_decode" "double")
(set_attr "bdver1_decode" "direct")
(set_attr "mode" "SI")])
@@ -8508,12 +8557,54 @@
(set_attr "length_immediate" "0")
(set (attr "athlon_decode")
(if_then_else (eq_attr "cpu" "athlon")
- (const_string "vector")
- (const_string "double")))
+ (const_string "vector")
+ (const_string "double")))
(set_attr "amdfam10_decode" "double")
(set_attr "bdver1_decode" "direct")
(set_attr "mode" "SI")])
+;; Highpart multiplication peephole2s to tweak register allocation.
+;; mov %rdx,imm; mov %rax,%rdi; imulq %rdx -> mov %rax,imm; imulq %rdi
+(define_peephole2
+ [(set (match_operand:SWI48 0 "general_reg_operand")
+ (match_operand:SWI48 1 "immediate_operand"))
+ (set (match_operand:SWI48 2 "general_reg_operand")
+ (match_operand:SWI48 3 "general_reg_operand"))
+ (parallel [(set (match_operand:SWI48 4 "general_reg_operand")
+ (any_mul_highpart:SWI48 (match_dup 2) (match_dup 0)))
+ (clobber (match_dup 2))
+ (clobber (reg:CC FLAGS_REG))])]
+ "REGNO (operands[0]) != REGNO (operands[2])
+ && REGNO (operands[0]) != REGNO (operands[3])
+ && (REGNO (operands[0]) == REGNO (operands[4])
+ || peep2_reg_dead_p (3, operands[0]))"
+ [(set (match_dup 2) (match_dup 1))
+ (parallel [(set (match_dup 4)
+ (any_mul_highpart:SWI48 (match_dup 2) (match_dup 3)))
+ (clobber (match_dup 2))
+ (clobber (reg:CC FLAGS_REG))])])
+
+(define_peephole2
+ [(set (match_operand:SI 0 "general_reg_operand")
+ (match_operand:SI 1 "immediate_operand"))
+ (set (match_operand:SI 2 "general_reg_operand")
+ (match_operand:SI 3 "general_reg_operand"))
+ (parallel [(set (match_operand:DI 4 "general_reg_operand")
+ (zero_extend:DI
+ (any_mul_highpart:SI (match_dup 2) (match_dup 0))))
+ (clobber (match_dup 2))
+ (clobber (reg:CC FLAGS_REG))])]
+ "REGNO (operands[0]) != REGNO (operands[2])
+ && REGNO (operands[0]) != REGNO (operands[3])
+ && (REGNO (operands[0]) == REGNO (operands[4])
+ || peep2_reg_dead_p (3, operands[0]))"
+ [(set (match_dup 2) (match_dup 1))
+ (parallel [(set (match_dup 4)
+ (zero_extend:DI
+ (any_mul_highpart:SI (match_dup 2) (match_dup 3))))
+ (clobber (match_dup 2))
+ (clobber (reg:CC FLAGS_REG))])])
+
;; The patterns that match these are at the end of this file.
(define_expand "mulxf3"
diff --git a/gcc/testsuite/gcc.target/i386/smuldi3_highpart.c
b/gcc/testsuite/gcc.target/i386/smuldi3_highpart.c
new file mode 100644
index 0000000..8bbd5f5
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/smuldi3_highpart.c
@@ -0,0 +1,11 @@
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-O2" } */
+typedef int __attribute ((mode(TI))) ti_t;
+
+long foo(long x)
+{
+ return ((ti_t)x * 19065) >> 72;
+}
+
+/* { dg-final { scan-assembler "movl\[ \\t]+\\\$19065, %eax" } } */
+/* { dg-final { scan-assembler-times "movq" 1 } } */
