This patch adds a convenient post-reload splitter for setting/updating
the highpart of a TImode variable, using the recently added
split_double_concat infrastructure.
For the new test case below:
__int128 foo(__int128 x, unsigned long long y)
{
__int128 t = (__int128)y << 64;
__int128 r = (x & ~0ull) | t;
return r;
}
mainline GCC with -O2 currently generates:
foo: movq %rdi, %rcx
xorl %eax, %eax
xorl %edi, %edi
orq %rcx, %rax
orq %rdi, %rdx
ret
with this patch, GCC instead now generates the much better:
foo: movq %rdi, %rcx
movq %rcx, %rax
ret
[which interestingly shows the deeper (ABI) issue that I'm trying
to fix, this new define_insn_and_split being the next piece].
It turns out that the -m32 equivalent of this testcase, already
avoids using explict orl/xor instructions, as it gets optimized
(in combine) by a completely different path. Given that this idiom
isn't seen in 32-bit code (and therefore this pattern wouldn't match),
and also that the shorter 32-bit AND bitmask is represented as a
CONST_INT rather than a CONST_WIDE_INT, this new define_insn_and_split
is implemented for just TARGET_64BIT rather than contort a "generic"
implementation using DWI mode iterators.
This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
and make -k check, both with and without --target_board=unix{-m32},
with no new failures. Ok for mainline? Please let me know if you'd
prefer a different pattern name [insv seemed better than mov].
2023-01-05 Roger Sayle <ro...@nextmovesoftware.com>
gcc/ChangeLog
* config/i386/i386.md (any_or_plus): Move definition earlier.
(*insvti_highpart_1): New define_insn_and_split to overwrite
(insv) the highpart of a TImode register/memory.
gcc/testsuite/ChangeLog
* gcc.target/i386/insvti_highpart-1.c: New test case.
Thanks in advance,
Roger
--
diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index 890c4c8..9f3c62b 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -3401,6 +3401,31 @@
"mov{b}\t{%h1, %h0|%h0, %h1}"
[(set_attr "type" "imov")
(set_attr "mode" "QI")])
+
+(define_code_iterator any_or_plus [plus ior xor])
+(define_insn_and_split "*insvti_highpart_1"
+ [(set (match_operand:TI 0 "nonimmediate_operand" "=ro,r,r,&r")
+ (any_or_plus:TI
+ (and:TI
+ (match_operand:TI 1 "nonimmediate_operand" "r,m,r,m")
+ (match_operand:TI 3 "const_scalar_int_operand" "n,n,n,n"))
+ (ashift:TI
+ (zero_extend:TI
+ (match_operand:DI 2 "nonimmediate_operand" "r,r,m,m"))
+ (const_int 64))))]
+ "TARGET_64BIT
+ && CONST_WIDE_INT_P (operands[3])
+ && CONST_WIDE_INT_NUNITS (operands[3]) == 2
+ && CONST_WIDE_INT_ELT (operands[3], 0) == -1
+ && CONST_WIDE_INT_ELT (operands[3], 1) == 0"
+ "#"
+ "&& reload_completed"
+ [(clobber (const_int 0))]
+{
+ operands[4] = gen_lowpart (DImode, operands[1]);
+ split_double_concat (TImode, operands[0], operands[4], operands[2]);
+ DONE;
+})
;; Floating point push instructions.
@@ -11418,7 +11443,6 @@
(set_attr "mode" "QI")])
;; Split DST = (HI<<32)|LO early to minimize register usage.
-(define_code_iterator any_or_plus [plus ior xor])
(define_insn_and_split "*concat<mode><dwi>3_1"
[(set (match_operand:<DWI> 0 "nonimmediate_operand" "=ro,r")
(any_or_plus:<DWI>
diff --git a/gcc/testsuite/gcc.target/i386/insvti_highpart-1.c
b/gcc/testsuite/gcc.target/i386/insvti_highpart-1.c
new file mode 100644
index 0000000..4ae9ccf
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/insvti_highpart-1.c
@@ -0,0 +1,12 @@
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-O2" } */
+
+__int128 foo(__int128 x, unsigned long long y)
+{
+ __int128 t = (__int128)y << 64;
+ __int128 r = (x & ~0ull) | t;
+ return r;
+}
+
+/* { dg-final { scan-assembler-not "xorl" } } */
+/* { dg-final { scan-assembler-not "orq" } } */
