Starting with r16-4438-ga93f80feeef744, the edges started to be sorted
in ascending order. Thus the most likely branches were deprioritized
instead of optimized to fallthroughs.
Fix by restoring the sorting order prior to r16-4438-ga93f80feeef744.
There are no regressions for C and C++ on x86_64-pc-linux-gnu.
The new tests fail for the respective targets without this patch, and
pass with it.
PR rtl-optimization/122675
gcc/ChangeLog:
* bb-reorder.cc (edge_order): Fix BB edge ordering to be
descending.
gcc/testsuite/ChangeLog:
* gcc.target/aarch64/pr122675-1.c: New test.
* gcc.target/i386/pr122675-1.c: New test.
* gcc.target/riscv/pr122675-1.c: New test.
Signed-off-by: Dimitar Dimitrov <[email protected]>
---
Changes since v1:
- Added tests utilizing check-function-bodies, per suggestion from
Andrew Pinski.
gcc/bb-reorder.cc | 7 +++-
gcc/testsuite/gcc.target/aarch64/pr122675-1.c | 31 ++++++++++++++
gcc/testsuite/gcc.target/i386/pr122675-1.c | 33 +++++++++++++++
gcc/testsuite/gcc.target/riscv/pr122675-1.c | 42 +++++++++++++++++++
4 files changed, 112 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/gcc.target/aarch64/pr122675-1.c
create mode 100644 gcc/testsuite/gcc.target/i386/pr122675-1.c
create mode 100644 gcc/testsuite/gcc.target/riscv/pr122675-1.c
diff --git a/gcc/bb-reorder.cc b/gcc/bb-reorder.cc
index e4efdee0b16..43fa019984a 100644
--- a/gcc/bb-reorder.cc
+++ b/gcc/bb-reorder.cc
@@ -2392,7 +2392,12 @@ edge_order (const void *ve1, const void *ve2)
gcov_type gc1 = c1.initialized_p () ? c1.to_gcov_type () : 0;
gcov_type gc2 = c2.initialized_p () ? c2.to_gcov_type () : 0;
gcov_type m = MAX (gc1, gc2);
- return (m == gc1) - (m == gc2);
+ /* While gcc_stablesort sorts in ascending order, the edges should
+ be sorted in descending order of their execution frequency.
+ So return a reversed comparison. Expressed with a spaceship operator:
+ return gc2 <=> gc1;
+ */
+ return (m == gc2) - (m == gc1);
}
/* Reorder basic blocks using the "simple" algorithm. This tries to
diff --git a/gcc/testsuite/gcc.target/aarch64/pr122675-1.c
b/gcc/testsuite/gcc.target/aarch64/pr122675-1.c
new file mode 100644
index 00000000000..8d2982ac21e
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/pr122675-1.c
@@ -0,0 +1,31 @@
+/* Verify that the most likely BB edges are optimized as fallthroughs. */
+/* { dg-do compile } */
+/* { dg-options "-O1 -fno-pic -mtune=generic -march=armv8-a" } */
+/* Keep labels and directives ('.cfi_startproc', '.cfi_endproc'). */
+/* { dg-final { check-function-bodies "**" "" "" { target *-*-* } {^\t?\.} } }
*/
+
+/*
+**test:
+**.LFB[0-9]+:
+** .cfi_startproc
+**...
+** cbz w0, .L[0-9]*
+**...
+** bl f1
+**...
+** ret
+**.L[0-9]+:
+**...
+** ret
+**...
+*/
+
+int f1(void);
+
+int test(int a)
+{
+ if (__builtin_expect(!!a, 1)) {
+ return f1();
+ }
+ return a;
+}
diff --git a/gcc/testsuite/gcc.target/i386/pr122675-1.c
b/gcc/testsuite/gcc.target/i386/pr122675-1.c
new file mode 100644
index 00000000000..fb41f5b2788
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr122675-1.c
@@ -0,0 +1,33 @@
+/* Verify that the most likely BB edges are optimized as fallthroughs. */
+/* { dg-do compile } */
+/* { dg-options "-O1 -fno-pic -march=x86-64 -mtune=generic
-mgeneral-regs-only" } */
+/* Keep labels and directives ('.cfi_startproc', '.cfi_endproc'). */
+/* { dg-final { check-function-bodies "**" "" "" { target lp64 } {^\t?\.} } }
*/
+
+/*
+**test:
+**.LFB[0-9]+:
+** .cfi_startproc
+** testl %edi, %edi
+** je .L[0-9]*
+** subq \$[0-9]*, %rsp
+** .cfi_def_cfa_offset [0-9]*
+** call f1
+** addq \$[0-9]*, %rsp
+** .cfi_def_cfa_offset [0-9]*
+** ret
+**.L[0-9]+:
+** movl %edi, %eax
+** ret
+**...
+*/
+
+int f1(void);
+
+int test(int a)
+{
+ if (__builtin_expect(!!a, 1)) {
+ return f1();
+ }
+ return a;
+}
diff --git a/gcc/testsuite/gcc.target/riscv/pr122675-1.c
b/gcc/testsuite/gcc.target/riscv/pr122675-1.c
new file mode 100644
index 00000000000..6f49ef3b5d8
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/pr122675-1.c
@@ -0,0 +1,42 @@
+/* Verify that the most likely BB edges are optimized as fallthroughs. */
+/* { dg-do compile } */
+/* { dg-options "-O1 -fno-pic -march=rv64gc -mabi=lp64d" } */
+/* Keep labels and directives ('.cfi_startproc', '.cfi_endproc'). */
+/* { dg-final { check-function-bodies "**" "" "" { target *-*-* } {^\t?\.} } }
*/
+
+/*
+**test:
+**...
+**.LFB[0-9]+:
+**...
+** .cfi_startproc
+**...
+** beq a0,zero,.L[0-9]*
+**...
+** call f1
+**...
+** (
+** jr ra
+** |
+** ret
+** )
+**...
+**.L[0-9]+:
+**...
+** (
+** jr ra
+** |
+** ret
+** )
+**...
+*/
+
+int f1(void);
+
+int test(int a)
+{
+ if (__builtin_expect(!!a, 1)) {
+ return f1();
+ }
+ return a;
+}
--
2.51.1
