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[PATCH][AArch64] Improve bit-test-branch pattern to avoid unnecessary register clobber
- From: Jiong Wang <jiong dot wang at arm dot com>
- To: "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>
- Date: Mon, 15 Dec 2014 15:36:08 +0000
- Subject: [PATCH][AArch64] Improve bit-test-branch pattern to avoid unnecessary register clobber
- Authentication-results: sourceware.org; auth=none
from the discussion here
https://gcc.gnu.org/ml/gcc-patches/2014-11/msg01949.html
the other problem it exposed is the unnecessary clobber of register x19
which
is a callee-saved register, then there are unnecessary push/pop in
pro/epilogue.
the reason comes from the following pattern:
(define_insn "tb<optab><mode>1"
(define_insn "cb<optab><mode>1"
they always declare "(clobber (match_scratch:DI 3 "=r"))" while that
register is
used only when "get_attr_length (insn) == 8".
actually, we could clobber CC register instead of scratch register to
avoid wasting
of general purpose registers.
this patch fix this, and give slightly improvement on spec2k.
bootstrap OK, no regression on aarch64 bare-metal.
ok for trunk?
the testcase included in the patch is for verification purpose only.
it could verify the long branch situation, while because of the code is
very big,
it takes a couple of seconds to compile. will not commit it.
gcc/
2014-12-15 Ramana Radhakrishnan ramana.radhakrishnan@arm.com
Jiong Wang jiong.wang@arm.com
* config/aarch64/aarch64.md (tb<optab><mode>1): Clobber CC reg
instead of scratch reg.
(cb<optab><mode>1): Likewise.
* config/aarch64/iterators.md (bcond): New define_code_attr.
diff --git a/gcc/config/aarch64/aarch64.md b/gcc/config/aarch64/aarch64.md
index 597ff8c..abf8e3f 100644
--- a/gcc/config/aarch64/aarch64.md
+++ b/gcc/config/aarch64/aarch64.md
@@ -466,13 +466,20 @@
(const_int 0))
(label_ref (match_operand 2 "" ""))
(pc)))
- (clobber (match_scratch:DI 3 "=r"))]
+ (clobber (reg:CC CC_REGNUM))]
""
- "*
- if (get_attr_length (insn) == 8)
- return \"ubfx\\t%<w>3, %<w>0, %1, #1\;<cbz>\\t%<w>3, %l2\";
- return \"<tbz>\\t%<w>0, %1, %l2\";
- "
+ {
+ if (get_attr_length (insn) == 8)
+ {
+ char buf[64];
+ uint64_t val = ((uint64_t) 1) << UINTVAL (operands[1]);
+ sprintf (buf, "tst\t%%<w>0, %"PRId64, val);
+ output_asm_insn (buf, operands);
+ return "<bcond>\t%l2";
+ }
+ else
+ return "<tbz>\t%<w>0, %1, %l2";
+ }
[(set_attr "type" "branch")
(set (attr "length")
(if_then_else (and (ge (minus (match_dup 2) (pc)) (const_int -32768))
@@ -486,13 +493,21 @@
(const_int 0))
(label_ref (match_operand 1 "" ""))
(pc)))
- (clobber (match_scratch:DI 2 "=r"))]
+ (clobber (reg:CC CC_REGNUM))]
""
- "*
- if (get_attr_length (insn) == 8)
- return \"ubfx\\t%<w>2, %<w>0, <sizem1>, #1\;<cbz>\\t%<w>2, %l1\";
- return \"<tbz>\\t%<w>0, <sizem1>, %l1\";
- "
+ {
+ if (get_attr_length (insn) == 8)
+ {
+ char buf[64];
+ uint64_t val = ((uint64_t ) 1)
+ << (GET_MODE_SIZE (<MODE>mode) * BITS_PER_UNIT - 1);
+ sprintf (buf, "tst\t%%<w>0, %"PRId64, val);
+ output_asm_insn (buf, operands);
+ return "<bcond>\t%l1";
+ }
+ else
+ return "<tbz>\t%<w>0, <sizem1>, %l1";
+ }
[(set_attr "type" "branch")
(set (attr "length")
(if_then_else (and (ge (minus (match_dup 1) (pc)) (const_int -32768))
diff --git a/gcc/config/aarch64/iterators.md b/gcc/config/aarch64/iterators.md
index 7dd3917..bd144f9 100644
--- a/gcc/config/aarch64/iterators.md
+++ b/gcc/config/aarch64/iterators.md
@@ -823,6 +823,9 @@
(smax "s") (umax "u")
(smin "s") (umin "u")])
+;; Emit conditional branch instructions.
+(define_code_attr bcond [(eq "beq") (ne "bne") (lt "bne") (ge "beq")])
+
;; Emit cbz/cbnz depending on comparison type.
(define_code_attr cbz [(eq "cbz") (ne "cbnz") (lt "cbnz") (ge "cbz")])
diff --git a/gcc/testsuite/gcc.target/aarch64/long_range_bit_test_branch_1.c b/gcc/testsuite/gcc.target/aarch64/long_range_bit_test_branch_1.c
new file mode 100644
index 0000000..d4782e9
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/long_range_bit_test_branch_1.c
@@ -0,0 +1,166 @@
+int dec (int);
+
+#define CASE_ENTRY(n) \
+ case n: \
+ sum = a / n; \
+ sum = sum * (n - 1); \
+ sum = dec (sum); \
+ sum = sum / (n + 1); \
+ sum = dec (sum); \
+ sum = sum / (n + 2); \
+ sum = dec (sum); \
+ sum = sum / (n + 3); \
+ sum = dec (sum); \
+ sum = sum / (n + 4); \
+ sum = dec (sum); \
+ sum = sum / (n + 5); \
+ sum = dec (sum); \
+ sum = sum / (n + 6); \
+ sum = dec (sum); \
+ sum = sum / (n + 7); \
+ sum = dec (sum); \
+ sum = sum / (n + 8); \
+ sum = dec (sum); \
+ sum = sum / (n + 9); \
+ sum = dec (sum); \
+ sum = sum / (n + 10); \
+ sum = dec (sum); \
+ sum = sum / (n + 11); \
+ sum = dec (sum); \
+ sum = sum / (n + 12); \
+ sum = dec (sum); \
+ sum = sum / (n + 13); \
+ sum = dec (sum); \
+ sum = sum / (n + 14); \
+ sum = dec (sum); \
+ sum = sum / (n + 15); \
+ sum = dec (sum); \
+ sum = sum / (n + 16); \
+ sum = dec (sum); \
+ sum = sum / (n + 17); \
+ sum = dec (sum); \
+ sum = sum / (n + 18); \
+ sum = dec (sum); \
+ sum = sum / (n + 19); \
+ sum = dec (sum); \
+ sum = sum / (n + 20); \
+ sum = dec (sum); \
+ sum = sum / (n + 21); \
+ sum = dec (sum); \
+ sum = sum / (n + 22); \
+ sum = dec (sum); \
+ sum = sum / (n + 23); \
+ sum = dec (sum); \
+ sum = sum / (n + 24); \
+ sum = dec (sum); \
+ sum = sum / (n + 25); \
+ sum = dec (sum); \
+ sum = sum / (n + 26); \
+ sum = dec (sum); \
+ sum = sum / (n + 27); \
+ sum = dec (sum); \
+ sum = sum / (n + 28); \
+ sum = dec (sum); \
+ sum = sum / (n + 29); \
+ sum = dec (sum); \
+ sum = sum / (n + 30); \
+ sum = dec (sum); \
+ sum = sum / (n + 31); \
+ break;
+
+int
+cbranch (int a, int b, int c, int d, long long addend)
+{
+ long long sum;
+ if (a & 0x2)
+ {
+start:
+ sum = b * c;
+ sum = sum + b + c;
+#ifdef CB
+ if (sum < 0)
+ goto start;
+#endif
+ }
+ else
+ {
+ switch (a/d)
+ {
+ CASE_ENTRY (1)
+ CASE_ENTRY (2)
+ CASE_ENTRY (3)
+ CASE_ENTRY (4)
+ CASE_ENTRY (5)
+ CASE_ENTRY (6)
+ CASE_ENTRY (7)
+ CASE_ENTRY (8)
+ CASE_ENTRY (9)
+ CASE_ENTRY (10)
+ CASE_ENTRY (11)
+ CASE_ENTRY (12)
+ CASE_ENTRY (13)
+ CASE_ENTRY (14)
+ CASE_ENTRY (15)
+ CASE_ENTRY (16)
+ CASE_ENTRY (17)
+ CASE_ENTRY (18)
+ CASE_ENTRY (19)
+ CASE_ENTRY (20)
+ CASE_ENTRY (21)
+ CASE_ENTRY (22)
+ CASE_ENTRY (23)
+ CASE_ENTRY (24)
+ CASE_ENTRY (25)
+ CASE_ENTRY (26)
+ CASE_ENTRY (27)
+ CASE_ENTRY (28)
+ CASE_ENTRY (29)
+ CASE_ENTRY (30)
+ CASE_ENTRY (31)
+ CASE_ENTRY (32)
+ CASE_ENTRY (33)
+ CASE_ENTRY (34)
+ CASE_ENTRY (35)
+ CASE_ENTRY (36)
+ CASE_ENTRY (37)
+ CASE_ENTRY (38)
+ CASE_ENTRY (39)
+ CASE_ENTRY (40)
+ CASE_ENTRY (41)
+ CASE_ENTRY (42)
+ CASE_ENTRY (43)
+ CASE_ENTRY (44)
+ CASE_ENTRY (45)
+ CASE_ENTRY (46)
+ CASE_ENTRY (47)
+ CASE_ENTRY (48)
+ CASE_ENTRY (49)
+ CASE_ENTRY (50)
+ CASE_ENTRY (51)
+ CASE_ENTRY (52)
+ CASE_ENTRY (53)
+ CASE_ENTRY (54)
+ CASE_ENTRY (55)
+ CASE_ENTRY (56)
+ CASE_ENTRY (57)
+ CASE_ENTRY (58)
+ CASE_ENTRY (59)
+ CASE_ENTRY (60)
+ CASE_ENTRY (61)
+ CASE_ENTRY (62)
+ CASE_ENTRY (63)
+ CASE_ENTRY (64)
+ }
+
+#ifdef CB
+ if (sum < 0)
+ goto start;
+#else
+
+ if (sum & 0x2000000000)
+ goto start;
+#endif
+ }
+
+ return sum;
+}