testcase: Add testcase for shrink wrapping of vector<int>::push_back [PR118502]

LLVM folks noticed that GCC was shrink wrapping the call to vector<int>::push_back.
So I thought it was a good idea to commit a testcase to make sure GCC does not regress
in this area unknowning.

Note the shrink wrapping started with r15-1619-g3b9b8d6cfdf593.
Note this enables the testcase for x86_64 (!ia32), powerpc, aarch64 and riscv which I tested
via godbolt to see the shrink wrapping occurs. Also tested the testcase for both
x86_64-linux-gnu and aarch64-linux-gnu to make sure I got the target selects correct.

Changes since v1:
* v2: Fix some comments typos that was mentioned in the bug report.

	PR rtl-optimization/118502

gcc/testsuite/ChangeLog:

	* g++.dg/opt/shrink-wrapping-vector-1.C: New test.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>

diff --git a/gcc/testsuite/g++.dg/opt/shrink-wrapping-vector-1.C b/gcc/testsuite/g++.dg/opt/shrink-wrapping-vector-1.C
new file mode 100644 (file)
index 0000000..8b1ad53
--- /dev/null
+++ b/gcc/testsuite/g++.dg/opt/shrink-wrapping-vector-1.C
@@ -0,0 +1,17 @@
+// { dg-do compile { target { { { i?86-*-* x86_64-*-* } && { ! ia32 } } || { powerpc*-*-* aarch64*-*-* riscv*-*-* }  } } }
+// { dg-options "-O2  -fdump-rtl-pro_and_epilogue"  }
+// { dg-skip-if "requires hosted libstdc++ for vector" { ! hostedlib } }
+
+// PR rtl-optimization/118502
+
+// The shrink-wrapping should happen around the slow path of vector<int>::push_back,
+// The fast path is just checking if there is enough space and doing a few stores.
+// We want to verify that shrink wrapping always happens.
+
+#include <vector>
+
+void push_back(std::vector<int>& xs, unsigned char x) {
+    xs.push_back(x);
+}
+
+/* { dg-final { scan-rtl-dump "Performing shrink-wrapping" "pro_and_epilogue" } } */