On Wed, Feb 25, 2026 at 11:03 PM Netanel Komm <[email protected]> wrote: > > This patch allows the GIMPLE folder to transform __builtin_mempcpy into > __builtin_memcpy > in cases where the return value is ignored. This is beneficial because most > targets have > an efficient implementation for memcpy. > > Existing tests that relied on the unfolded mempcpy have been duplicated - one > version now > takes the folded mempcpy into account, and the other intentionally prevents > the folding > from happening. > > Bootstrapped and regression tested on x86_64-linux-gnu.
LGTM, but this has to wait for stage1. One nit below > PR tree-optimization/93556 > > gcc/ChangeLog: > > * gimple-fold.cc (gimple_fold_builtin_mempcpy): New function. > (gimple_fold_builtin): Handle BUILT_IN_MEMPCPY. > > gcc/testsuite/ChangeLog: > > * gcc.dg/pr79223.c: Rename to gcc.dg/pr79223-1.c and update scans. > * gcc.dg/tree-prof/val-prof-7.c: Rename to > gcc.dg/tree-prof/val-prof-7-1.c and update scans. > * gcc.dg/tree-ssa/builtins-folding-gimple-3.c: Update scans. > * gcc.dg/builtin-mempcpy-1.c: New test. > * gcc.dg/builtin-mempcpy-2.c: New test. > * gcc.dg/pr79223-2.c: New test. > * gcc.dg/tree-prof/val-prof-7-2.c: New test. > * gcc.dg/tree-ssa/builtins-folding-gimple-4.c: New test. > > Signed-off-by: Netanel Komm <[email protected]> > --- > gcc/gimple-fold.cc | 24 +++++- > gcc/testsuite/gcc.dg/builtin-mempcpy-1.c | 9 ++ > gcc/testsuite/gcc.dg/builtin-mempcpy-2.c | 39 +++++++++ > .../gcc.dg/{pr79223.c => pr79223-1.c} | 2 +- > gcc/testsuite/gcc.dg/pr79223-2.c | 38 +++++++++ > gcc/testsuite/gcc.dg/tree-prof/val-prof-7-1.c | 82 +++++++++++++++++++ > .../{val-prof-7.c => val-prof-7-2.c} | 2 +- > .../tree-ssa/builtins-folding-gimple-3.c | 5 +- > .../tree-ssa/builtins-folding-gimple-4.c | 45 ++++++++++ > 9 files changed, 240 insertions(+), 6 deletions(-) > create mode 100644 gcc/testsuite/gcc.dg/builtin-mempcpy-1.c > create mode 100644 gcc/testsuite/gcc.dg/builtin-mempcpy-2.c > rename gcc/testsuite/gcc.dg/{pr79223.c => pr79223-1.c} (86%) > create mode 100644 gcc/testsuite/gcc.dg/pr79223-2.c > create mode 100644 gcc/testsuite/gcc.dg/tree-prof/val-prof-7-1.c > rename gcc/testsuite/gcc.dg/tree-prof/{val-prof-7.c => val-prof-7-2.c} (97%) > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/builtins-folding-gimple-4.c > > diff --git a/gcc/gimple-fold.cc b/gcc/gimple-fold.cc > index bc8540a8c5c..f870a7feb51 100644 > --- a/gcc/gimple-fold.cc > +++ b/gcc/gimple-fold.cc > @@ -3339,6 +3339,24 @@ gimple_fold_builtin_stpcpy (gimple_stmt_iterator *gsi) > return true; > } > > +static bool > +gimple_fold_builtin_mempcpy (gimple_stmt_iterator *gsi) > +{ > + gcall *stmt = as_a <gcall *> (gsi_stmt (*gsi)); > + > + if (gimple_call_lhs (stmt) == NULL_TREE) > + { > + tree fn = builtin_decl_implicit (BUILT_IN_MEMCPY); I think you can use builtin_decl_explicit as we require memcpy to be available. > + if (!fn) > + return false; > + gimple_call_set_fndecl (stmt, fn); > + fold_stmt (gsi); > + return true; > + } > + > + return false; > +} > + > /* Fold a call EXP to {,v}snprintf having NARGS passed as ARGS. Return > NULL_TREE if a normal call should be emitted rather than expanding > the function inline. FCODE is either BUILT_IN_SNPRINTF_CHK or > @@ -5387,8 +5405,12 @@ gimple_fold_builtin (gimple_stmt_iterator *gsi) > return gimple_fold_builtin_memset (gsi, > gimple_call_arg (stmt, 1), > gimple_call_arg (stmt, 2)); > - case BUILT_IN_MEMCPY: > case BUILT_IN_MEMPCPY: > + if (gimple_fold_builtin_memory_op (gsi, gimple_call_arg (stmt, 0), > + gimple_call_arg (stmt, 1), fcode)) > + return true; > + return gimple_fold_builtin_mempcpy (gsi); > + case BUILT_IN_MEMCPY: > case BUILT_IN_MEMMOVE: > return gimple_fold_builtin_memory_op (gsi, gimple_call_arg (stmt, 0), > gimple_call_arg (stmt, 1), fcode); > diff --git a/gcc/testsuite/gcc.dg/builtin-mempcpy-1.c > b/gcc/testsuite/gcc.dg/builtin-mempcpy-1.c > new file mode 100644 > index 00000000000..19d9a224657 > --- /dev/null > +++ b/gcc/testsuite/gcc.dg/builtin-mempcpy-1.c > @@ -0,0 +1,9 @@ > +/* { dg-do compile } */ > +/* { dg-options "-fdump-tree-lower" } */ > + > +/* Basic MRE from bug report */ > +void test_bare (void *d, const void *s, __SIZE_TYPE__ n) { > + __builtin_mempcpy (d, s, n); > +} > + > +/* { dg-final { scan-tree-dump "__builtin_memcpy" "lower" } } */ > diff --git a/gcc/testsuite/gcc.dg/builtin-mempcpy-2.c > b/gcc/testsuite/gcc.dg/builtin-mempcpy-2.c > new file mode 100644 > index 00000000000..65f80f97f4f > --- /dev/null > +++ b/gcc/testsuite/gcc.dg/builtin-mempcpy-2.c > @@ -0,0 +1,39 @@ > +/* { dg-do compile } */ > +/* { dg-options "-O1 -fdump-tree-optimized" } */ > + > +/* Indirectly unused result */ > +void test_unused_indirect (void *d, const void *s, __SIZE_TYPE__ n) { > + void *a = __builtin_mempcpy (d, s, n); > + void *b = a; > +} > + > +/* Simple used result (in statement) */ > +void *test_used_simple (void *d, const void *s, __SIZE_TYPE__ n) { > + return __builtin_mempcpy (d, s, n); > +} > + > +/* More complicated used result (in expression) */ > +__SIZE_TYPE__ test_used_in_expr (char *d, const char *s, __SIZE_TYPE__ n) { > + return (char *)__builtin_mempcpy (d, s, n) - d; > +} > + > +/* Unused in all paths */ > +void *test_unused_indirect2 (void *d, const void *s, __SIZE_TYPE__ n) { > + void *a = __builtin_mempcpy (d, s, n); > + if (n > 20) { > + return (void *)20; > + } > + return (void *)7; > +} > + > +/* Used in at least one path */ > +void *test_maybe_used (void *d, const void *s, __SIZE_TYPE__ n) { > + void *a = __builtin_mempcpy (d, s, n); > + if (n > 20) { > + return a; > + } > + return (void *)0; > +} > + > +/* { dg-final { scan-tree-dump-times "__builtin_memcpy" 2 "optimized" } } */ > +/* { dg-final { scan-tree-dump-times "__builtin_mempcpy" 3 "optimized" } } */ > diff --git a/gcc/testsuite/gcc.dg/pr79223.c b/gcc/testsuite/gcc.dg/pr79223-1.c > similarity index 86% > rename from gcc/testsuite/gcc.dg/pr79223.c > rename to gcc/testsuite/gcc.dg/pr79223-1.c > index ef0dd1b7bc5..099d18333e8 100644 > --- a/gcc/testsuite/gcc.dg/pr79223.c > +++ b/gcc/testsuite/gcc.dg/pr79223-1.c > @@ -28,7 +28,7 @@ void test_memcpy (void) > > void test_mempcpy (void) > { > - mempcpy (d, s, range ()); /* { dg-warning ".mempcpy. writing 4 or more > bytes into a region of size 3 overflows the destination" } */ > + mempcpy (d, s, range ()); /* { dg-warning ".memcpy. writing 4 or more > bytes into a region of size 3 overflows the destination" } */ > } > > void test_memmove (void) > diff --git a/gcc/testsuite/gcc.dg/pr79223-2.c > b/gcc/testsuite/gcc.dg/pr79223-2.c > new file mode 100644 > index 00000000000..6e78b326671 > --- /dev/null > +++ b/gcc/testsuite/gcc.dg/pr79223-2.c > @@ -0,0 +1,38 @@ > +/* PR middle-end/79223 - missing -Wstringop-overflow on a memmove overflow > + { dg-do compile } > + { dg-additional-options "-O2 -Wall -Wno-array-bounds -std=gnu99" } */ > + > +typedef __SIZE_TYPE__ size_t; > + > +extern void* memcpy (void*, const void*, size_t); > +extern void* mempcpy (void*, const void*, size_t); > +extern void* memmove (void*, const void*, size_t); > + > +char d[3]; > +char s[4]; > +void *sink; > + > +size_t range (void) > +{ > + extern size_t size (); > + size_t n = size (); > + if (n <= sizeof d) > + return sizeof d + 1; > + > + return n; > +} > + > +void test_memcpy (void) > +{ > + memcpy (d, s, range ()); /* { dg-warning ".memcpy. writing 4 or more > bytes into a region of size 3 overflows the destination" } */ > +} > + > +void test_mempcpy (void) > +{ > + sink = mempcpy (d, s, range ()); /* { dg-warning ".mempcpy. writing 4 or > more bytes into a region of size 3 overflows the destination" } */ > +} > + > +void test_memmove (void) > +{ > + memmove (d + 1, d, range ()); /* { dg-warning ".memmove. writing 4 or > more bytes into a region of size 2 overflows the destination" } */ > +} > diff --git a/gcc/testsuite/gcc.dg/tree-prof/val-prof-7-1.c > b/gcc/testsuite/gcc.dg/tree-prof/val-prof-7-1.c > new file mode 100644 > index 00000000000..321eefa8207 > --- /dev/null > +++ b/gcc/testsuite/gcc.dg/tree-prof/val-prof-7-1.c > @@ -0,0 +1,82 @@ > +/* { dg-options "-O2 -fdump-ipa-profile-optimized -mtune=core2" } */ > +/* { dg-skip-if "" { ! { i?86-*-* x86_64-*-* } } } */ > + > +char *buffer1; > +char *buffer2; > + > +/* Bzero is not tested because it gets transformed into memset. */ > + > +#define DEFINE_TEST(N) \ > +__attribute__((noinline)) \ > +void memcpy_test_ ## N (int len) \ > +{ \ > + __builtin_memcpy (buffer1, buffer2, len); \ > +} \ > + \ > +__attribute__((noinline)) \ > +void mempcpy_test_ ## N (int len) \ > +{ \ > + __builtin_mempcpy (buffer1, buffer2, len); \ > +} \ > + \ > +__attribute__((noinline)) \ > +void memset_test_ ## N (int len) \ > +{ \ > + __builtin_memset (buffer1, 'c', len); \ > +} \ > +__attribute__((noinline)) \ > +void memmove_test_ ## N (int len) \ > +{ \ > + __builtin_memmove (buffer1, buffer2, len); \ > +} \ > + \ > +void test_stringops_ ## N(int len) \ > +{ \ > + memcpy_test_## N (len); \ > + mempcpy_test_ ## N (len); \ > + memset_test_ ## N (len); \ > + memmove_test_ ## N (len); \ > +} \ > + \ > +void test_stringops_with_values_ ## N (int common, int not_common) \ > +{ \ > + int i; \ > + for (i = 0; i < 1000; i++) \ > + { \ > + if (i > 990) \ > + test_stringops_ ## N (not_common); \ > + else \ > + test_stringops_ ## N (common); \ > + } \ > +} > + > +DEFINE_TEST(0); > +DEFINE_TEST(1); > +DEFINE_TEST(2); > + > +int main() { > + buffer1 = __builtin_malloc (1000); > + buffer2 = __builtin_malloc (1000); > + > + test_stringops_with_values_0 (8, 55); > + test_stringops_with_values_1 (55, 55); > + test_stringops_with_values_2 (257, 55); > + > + return 0; > +} > + > +/* { dg-final-use-not-autofdo { scan-ipa-dump "Transformation done: single > value 8 stringop for BUILT_IN_MEMCPY" "profile" } } */ > +/* { dg-final-use-not-autofdo { scan-ipa-dump "Transformation done: single > value 55 stringop for BUILT_IN_MEMCPY" "profile" } } */ > +/* { dg-final-use-not-autofdo { scan-ipa-dump-times "Transformation done: > single value 32 stringop for BUILT_IN_MEMCPY" 0 "profile" } } */ > + > +/* { dg-final-use-not-autofdo { scan-ipa-dump "Transformation done: single > value 8 stringop for BUILT_IN_MEMCPY" "profile" } } */ > +/* { dg-final-use-not-autofdo { scan-ipa-dump "Transformation done: single > value 55 stringop for BUILT_IN_MEMCPY" "profile" } } */ > +/* { dg-final-use-not-autofdo { scan-ipa-dump-times "Transformation done: > single value 32 stringop for BUILT_IN_MEMPCPY" 0 "profile" } } */ > + > +/* { dg-final-use-not-autofdo { scan-ipa-dump "Transformation done: single > value 8 stringop for BUILT_IN_MEMSET" "profile" } } */ > +/* { dg-final-use-not-autofdo { scan-ipa-dump "Transformation done: single > value 55 stringop for BUILT_IN_MEMSET" "profile" } } */ > +/* { dg-final-use-not-autofdo { scan-ipa-dump-times "Transformation done: > single value 32 stringop for BUILT_IN_MEMSET" 0 "profile" } } */ > + > +/* { dg-final-use-not-autofdo { scan-ipa-dump "Transformation done: single > value 8 stringop for BUILT_IN_MEMMOVE" "profile" } } */ > +/* { dg-final-use-not-autofdo { scan-ipa-dump "Transformation done: single > value 55 stringop for BUILT_IN_MEMMOVE" "profile" } } */ > +/* { dg-final-use-not-autofdo { scan-ipa-dump-times "Transformation done: > single value 32 stringop for BUILT_IN_MEMMOVE" 0 "profile" } } */ > diff --git a/gcc/testsuite/gcc.dg/tree-prof/val-prof-7.c > b/gcc/testsuite/gcc.dg/tree-prof/val-prof-7-2.c > similarity index 97% > rename from gcc/testsuite/gcc.dg/tree-prof/val-prof-7.c > rename to gcc/testsuite/gcc.dg/tree-prof/val-prof-7-2.c > index 5ddb1a88c29..1084a852fc3 100644 > --- a/gcc/testsuite/gcc.dg/tree-prof/val-prof-7.c > +++ b/gcc/testsuite/gcc.dg/tree-prof/val-prof-7-2.c > @@ -16,7 +16,7 @@ void memcpy_test_ ## N (int len) \ > __attribute__((noinline)) \ > void mempcpy_test_ ## N (int len) \ > { \ > - __builtin_mempcpy (buffer1, buffer2, len); \ > + void * volatile res = __builtin_mempcpy (buffer1, buffer2, len); \ > } \ > \ > __attribute__((noinline)) \ > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/builtins-folding-gimple-3.c > b/gcc/testsuite/gcc.dg/tree-ssa/builtins-folding-gimple-3.c > index 716be5b8094..0872cc52a7f 100644 > --- a/gcc/testsuite/gcc.dg/tree-ssa/builtins-folding-gimple-3.c > +++ b/gcc/testsuite/gcc.dg/tree-ssa/builtins-folding-gimple-3.c > @@ -38,6 +38,5 @@ AR (memmove, int, 2, INT_MAX, 1); > AR (mempcpy, short, 2, SHRT_MAX, 1); > AR (mempcpy, int, 2, INT_MAX, 1); > > -/* { dg-final { scan-tree-dump-times "builtin_memcpy" 8 "optimized" } } > - { dg-final { scan-tree-dump-times "builtin_memmove" 2 "optimized" } } > - { dg-final { scan-tree-dump-times "builtin_mempcpy" 2 "optimized" } } */ > +/* { dg-final { scan-tree-dump-times "builtin_memcpy" 10 "optimized" } } > + { dg-final { scan-tree-dump-times "builtin_memmove" 2 "optimized" } } */ > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/builtins-folding-gimple-4.c > b/gcc/testsuite/gcc.dg/tree-ssa/builtins-folding-gimple-4.c > new file mode 100644 > index 00000000000..0f0c577c64a > --- /dev/null > +++ b/gcc/testsuite/gcc.dg/tree-ssa/builtins-folding-gimple-4.c > @@ -0,0 +1,45 @@ > +/* PR 81908 - FAIL: gfortran.dg/alloc_comp_auto_array_2.f90 -O3 -g -m32 > + Test to verify that calls to memcpy et al. where the size is in a range > + with more than one valid value are not eliminated (this test complements > + builtins-folding-gimple-2.c). > + { dg-do compile } > + { dg-options "-O2 -Wall -fdump-tree-optimized" } */ > + > +#define SHRT_MAX __SHRT_MAX__ > +#define SHRT_MIN (-SHRT_MAX - 1) > +#define INT_MAX __INT_MAX__ > +#define INT_MIN (-INT_MAX - 1) > + > +#define UNIQUE_FUNCNAME(func, line) test_ ## func ## _ ## line > +#define FUNCNAME(func, line) UNIQUE_FUNCNAME (func, line) > + > +void *sink; > + > +#define AR(func, type, min, max, val) \ > + void __attribute__ ((noclone, noinline)) \ > + FUNCNAME (func, __LINE__) (char *d, const char *s, type n) \ > + { \ > + if ((type)min <= n && n <= (type)max) \ > + n = val; \ > + sink = __builtin_ ## func (d, s, n); > \ > + } typedef void DummyType > + > +AR (memcpy, short, SHRT_MIN, 0, 1); > +AR (memcpy, short, SHRT_MIN, 1, 2); > +AR (memcpy, short, 2, SHRT_MAX, 1); > + > +AR (memcpy, int, INT_MIN, 0, 1); > +AR (memcpy, int, INT_MIN, 1, 2); > +AR (memcpy, int, INT_MIN, 2, 3); > +AR (memcpy, int, 2, INT_MAX, 1); > +AR (memcpy, int, 2, INT_MAX, 1); > + > +AR (memmove, short, 2, SHRT_MAX, 1); > +AR (memmove, int, 2, INT_MAX, 1); > + > +AR (mempcpy, short, 2, SHRT_MAX, 1); > +AR (mempcpy, int, 2, INT_MAX, 1); > + > +/* { dg-final { scan-tree-dump-times "builtin_memcpy" 8 "optimized" } } > + { dg-final { scan-tree-dump-times "builtin_memmove" 2 "optimized" } } > + { dg-final { scan-tree-dump-times "builtin_mempcpy" 2 "optimized" } } */ > -- > 2.30.2 >
