From 1bd3a8af85356e64ec27309dba7fb2fca2343ffe Mon Sep 17 00:00:00 2001 From: Alex Coplan Date: Tue, 5 May 2020 10:33:02 +0100 Subject: [PATCH] aarch64: eliminate redundant zero extend after bitwise negation The attached patch eliminates a redundant zero extend from the AArch64 backend. Given the following C code: unsigned long long foo(unsigned a) { return ~a; } prior to this patch, AArch64 GCC at -O2 generates: foo: mvn w0, w0 uxtw x0, w0 ret but the uxtw is redundant, since the mvn clears the upper half of the x0 register. After applying this patch, GCC at -O2 gives: foo: mvn w0, w0 ret Testing: Added regression test which passes after applying the change to aarch64.md. Full bootstrap and regression on aarch64-linux with no additional failures. * config/aarch64/aarch64.md (*one_cmpl_zero_extend): New. * gcc.target/aarch64/mvn_zero_ext.c: New test. --- gcc/ChangeLog | 4 ++++ gcc/config/aarch64/aarch64.md | 9 +++++++++ gcc/testsuite/ChangeLog | 4 ++++ gcc/testsuite/gcc.target/aarch64/mvn_zero_ext.c | 15 +++++++++++++++ 4 files changed, 32 insertions(+) create mode 100644 gcc/testsuite/gcc.target/aarch64/mvn_zero_ext.c diff --git a/gcc/ChangeLog b/gcc/ChangeLog index cc076c8ea42..6a419757bf8 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,7 @@ +2020-05-05 Alex Coplan + + * config/aarch64/aarch64.md (*one_cmpl_zero_extend): New. + 2020-05-05 Jakub Jelinek PR tree-optimization/94800 diff --git a/gcc/config/aarch64/aarch64.md b/gcc/config/aarch64/aarch64.md index 8c8be3c2740..ff15505d455 100644 --- a/gcc/config/aarch64/aarch64.md +++ b/gcc/config/aarch64/aarch64.md @@ -4619,6 +4619,15 @@ (set_attr "arch" "*,simd")] ) +(define_insn "*one_cmpl_zero_extend" + [(set (match_operand:DI 0 "register_operand" "=r") + (zero_extend:DI + (not:SI (match_operand:SI 1 "register_operand" "r"))))] + "" + "mvn\\t%w0, %w1" + [(set_attr "type" "logic_reg")] +) + (define_insn "*one_cmpl_2" [(set (match_operand:GPI 0 "register_operand" "=r") (not:GPI (SHIFT:GPI (match_operand:GPI 1 "register_operand" "r") diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog index 2b487415846..e06bcf86212 100644 --- a/gcc/testsuite/ChangeLog +++ b/gcc/testsuite/ChangeLog @@ -1,3 +1,7 @@ +2020-05-05 Alex Coplan + + * gcc.target/aarch64/mvn_zero_ext.c: New test. + 2020-05-05 Jakub Jelinek PR tree-optimization/94800 diff --git a/gcc/testsuite/gcc.target/aarch64/mvn_zero_ext.c b/gcc/testsuite/gcc.target/aarch64/mvn_zero_ext.c new file mode 100644 index 00000000000..3cd2a2fb9fb --- /dev/null +++ b/gcc/testsuite/gcc.target/aarch64/mvn_zero_ext.c @@ -0,0 +1,15 @@ +/* { dg-do compile } */ +/* { dg-options "-O2" } */ + +/* +** foo: +** mvn w0, w0 +** ret +*/ +unsigned long long +foo (unsigned a) +{ + return ~a; +} + +/* { dg-final { check-function-bodies "**" "" "" } } */ -- 2.30.2