The stringop strategy selection algorithm falls back to a libcall strategy
when it exhausts its pool of available strategies. The memory area copy
function (memcpy) is not available from the system library for non-default
address spaces, so the compiler emits the most trivial byte-at-a-time
copy loop instead.
The compiler should instead emit an optimized copy loop as a fallback for
non-default address spaces.
PR target/111657
gcc/ChangeLog:
* config/i386/i386-expand.cc (alg_usable_p): Reject libcall
strategy for non-default address spaces.
(decide_alg): Use loop strategy as a fallback strategy for
non-default address spaces.
gcc/testsuite/ChangeLog:
* gcc.target/i386/pr111657.c: New test.
Bootstrapped and regression tested on x86_64-linux-gnu {,-m32}.
diff --git a/gcc/config/i386/i386-expand.cc b/gcc/config/i386/i386-expand.cc
index e42ff27c6ef..9a988347200 100644
--- a/gcc/config/i386/i386-expand.cc
+++ b/gcc/config/i386/i386-expand.cc
@@ -8320,6 +8320,11 @@ alg_usable_p (enum stringop_alg alg, bool memset, bool
have_as)
{
if (alg == no_stringop)
return false;
+ /* It is not possible to use a library call if we have non-default
+ address space. We can do better than the generic byte-at-a-time
+ loop, used as a fallback. */
+ if (alg == libcall && have_as)
+ return false;
if (alg == vector_loop)
return TARGET_SSE || TARGET_AVX;
/* Algorithms using the rep prefix want at least edi and ecx;
@@ -8494,8 +8499,12 @@ decide_alg (HOST_WIDE_INT count, HOST_WIDE_INT
expected_size,
gcc_assert (alg != libcall);
return alg;
}
+
+ /* Try to use some reasonable fallback algorithm. Note that for
+ non-default address spaces we default to a loop instead of
+ a libcall. */
return (alg_usable_p (algs->unknown_size, memset, have_as)
- ? algs->unknown_size : libcall);
+ ? algs->unknown_size : have_as ? loop : libcall);
}
/* Decide on alignment. We know that the operand is already aligned to ALIGN
diff --git a/gcc/testsuite/gcc.target/i386/pr111657.c
b/gcc/testsuite/gcc.target/i386/pr111657.c
new file mode 100644
index 00000000000..fe54fcae8cc
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr111657.c
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-rtl-expand -mno-sse" } */
+
+struct a { long arr[30]; };
+
+__seg_gs struct a m;
+void bar (struct a *dst) { *dst = m; }
+
+/* { dg-final { scan-rtl-dump-not "libcall" "expand" } } */
