This patch generalizes some of the patterns in i386.md that recognize
double word concatenation, so they handle sign_extend the same way that
they handle zero_extend in appropriate contexts.
As a motivating example consider the following function:
__int128 foo(long long x, unsigned long long y)
{
return ((__int128)x<<64) | y;
}
when compiled with -O2, x86_64 currently generates:
foo: movq %rdi, %rdx
xorl %eax, %eax
xorl %edi, %edi
orq %rsi, %rax
orq %rdi, %rdx
ret
with this patch we now generate (the same as if x is unsigned):
foo: movq %rsi, %rax
movq %rdi, %rdx
ret
Treating both extensions the same way using any_extend is valid as
the top (extended) bits are "unused" after the shift by 64 (or more).
In theory, the RTL optimizers might consider canonicalizing the form
of extension used in these cases, but zero_extend is faster on some
machines, whereas sign extension is supported via addressing modes on
others, so handling both in the machine description is probably best.
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?
2024-06-27 Roger Sayle <ro...@nextmovesoftware.com>
gcc/ChangeLog
* config/i386/i386.md (*concat<mode><dwi>3_3): Change zero_extend
to any_extend in first operand to left shift by mode precision.
(*concat<mode><dwi>3_4): Likewise.
(*concat<mode><dwi>3_6): Likewise.
gcc/testsuite/ChangeLog
* gcc.target/i386/concatditi-1.c: New test case.
Thanks in advance,
Roger
--
diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index fd48e76..b6ccb1e 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -13446,7 +13446,7 @@
[(set (match_operand:<DWI> 0 "nonimmediate_operand" "=ro,r,r,&r,x")
(any_or_plus:<DWI>
(ashift:<DWI>
- (zero_extend:<DWI>
+ (any_extend:<DWI>
(match_operand:DWIH 1 "nonimmediate_operand" "r,m,r,m,x"))
(match_operand:QI 2 "const_int_operand"))
(zero_extend:<DWI>
@@ -13473,7 +13473,7 @@
(zero_extend:<DWI>
(match_operand:DWIH 1 "nonimmediate_operand" "r,m,r,m"))
(ashift:<DWI>
- (zero_extend:<DWI>
+ (any_extend:<DWI>
(match_operand:DWIH 2 "nonimmediate_operand" "r,r,m,m"))
(match_operand:QI 3 "const_int_operand"))))]
"INTVAL (operands[3]) == <MODE_SIZE> * BITS_PER_UNIT"
@@ -13520,7 +13520,7 @@
[(set (match_operand:<DWI> 0 "nonimmediate_operand" "=r,o,o,r")
(any_or_plus:<DWI>
(ashift:<DWI>
- (zero_extend:<DWI>
+ (any_extend:<DWI>
(match_operand:DWIH 1 "nonimmediate_operand" "r,r,r,m"))
(match_operand:QI 2 "const_int_operand"))
(match_operand:<DWI> 3 "const_scalar_int_operand" "n,n,Wd,n")))]
diff --git a/gcc/testsuite/gcc.target/i386/concatditi-1.c
b/gcc/testsuite/gcc.target/i386/concatditi-1.c
new file mode 100644
index 0000000..25c2a95
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/concatditi-1.c
@@ -0,0 +1,10 @@
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-O2" } */
+
+__int128 foo(long long x, unsigned long long y)
+{
+ return ((__int128)x<<64) | y;
+}
+
+/* { dg-final { scan-assembler-not "xorl" } } */
+/* { dg-final { scan-assembler-not "orq" } } */
