From f76949cee9560d04d5417481dbcda5ca089c9ebc Mon Sep 17 00:00:00 2001 From: Jakub Jelinek Date: Tue, 13 Oct 2020 19:13:26 +0200 Subject: [PATCH] combine: Fix up simplify_shift_const_1 for nested ROTATEs [PR97386] The following testcases are miscompiled (the first one since my improvements to rotate discovery on GIMPLE, the other one for many years) because combiner optimizes nested ROTATEs with narrowing SUBREG in between (i.e. the outer rotate is performed in shorter precision than the inner one) to just one ROTATE of the rotated constant. While that (under certain conditions) can work for shifts, it can't work for rotates where we can only do that with rotates of the same precision. 2020-10-13 Jakub Jelinek PR rtl-optimization/97386 * combine.c (simplify_shift_const_1): Don't optimize nested ROTATEs if they have different modes. * gcc.c-torture/execute/pr97386-1.c: New test. * gcc.c-torture/execute/pr97386-2.c: New test. --- gcc/combine.c | 7 +++++-- .../gcc.c-torture/execute/pr97386-1.c | 16 +++++++++++++++ .../gcc.c-torture/execute/pr97386-2.c | 20 +++++++++++++++++++ 3 files changed, 41 insertions(+), 2 deletions(-) create mode 100644 gcc/testsuite/gcc.c-torture/execute/pr97386-1.c create mode 100644 gcc/testsuite/gcc.c-torture/execute/pr97386-2.c diff --git a/gcc/combine.c b/gcc/combine.c index c88382efbd3..4782e1d9dcc 100644 --- a/gcc/combine.c +++ b/gcc/combine.c @@ -11003,8 +11003,11 @@ simplify_shift_const_1 (enum rtx_code code, machine_mode result_mode, break; /* For ((int) (cstLL >> count)) >> cst2 just give up. Queuing up outer sign extension (often left and right shift) is - hardly more efficient than the original. See PR70429. */ - if (code == ASHIFTRT && int_mode != int_result_mode) + hardly more efficient than the original. See PR70429. + Similarly punt for rotates with different modes. + See PR97386. */ + if ((code == ASHIFTRT || code == ROTATE) + && int_mode != int_result_mode) break; rtx count_rtx = gen_int_shift_amount (int_result_mode, count); diff --git a/gcc/testsuite/gcc.c-torture/execute/pr97386-1.c b/gcc/testsuite/gcc.c-torture/execute/pr97386-1.c new file mode 100644 index 00000000000..c50e0380a65 --- /dev/null +++ b/gcc/testsuite/gcc.c-torture/execute/pr97386-1.c @@ -0,0 +1,16 @@ +/* PR rtl-optimization/97386 */ + +__attribute__((noipa)) unsigned char +foo (unsigned int c) +{ + return __builtin_bswap16 ((unsigned long long) (0xccccLLU << c | 0xccccLLU >> ((-c) & 63))); +} + +int +main () +{ + unsigned char x = foo (0); + if (__CHAR_BIT__ == 8 && __SIZEOF_SHORT__ == 2 && x != 0xcc) + __builtin_abort (); + return 0; +} diff --git a/gcc/testsuite/gcc.c-torture/execute/pr97386-2.c b/gcc/testsuite/gcc.c-torture/execute/pr97386-2.c new file mode 100644 index 00000000000..e61829d71ab --- /dev/null +++ b/gcc/testsuite/gcc.c-torture/execute/pr97386-2.c @@ -0,0 +1,20 @@ +/* PR rtl-optimization/97386 */ + +__attribute__((noipa)) unsigned +foo (int x) +{ + unsigned long long a = (0x800000000000ccccULL << x) | (0x800000000000ccccULL >> (64 - x)); + unsigned int b = a; + return (b << 24) | (b >> 8); +} + +int +main () +{ + if (__CHAR_BIT__ == 8 + && __SIZEOF_INT__ == 4 + && __SIZEOF_LONG_LONG__ == 8 + && foo (1) != 0x99000199U) + __builtin_abort (); + return 0; +} -- 2.30.2