ipa-sra: Don't change return type to void if there are musttail calls [PR119484]

The following testcase is rejected, because IPA-SRA decides to
turn bar.constprop call into bar.constprop.isra which returns void.
While there is no explicit lhs on the call, as it is a musttail call
the tailc pass checks if IPA-VRP returns singleton from that function
and the function returns the same value and in that case it still turns
it into a tail call.  This can't work with IPA-SRA changing it into
void returning function though.

The following patch fixes this by forcing returning the original type
if there are musttail calls.

2025-03-28  Jakub Jelinek  <jakub@redhat.com>

	PR ipa/119484
	* ipa-sra.cc (isra_analyze_call): Don't set m_return_ignored if
	gimple_call_must_tail_p even if it doesn't have lhs.

	* c-c++-common/pr119484.c: New test.

2 files changed, 26 insertions, 1 deletions

diff --git a/gcc/ipa-sra.cc b/gcc/ipa-sra.cc
index 5d1703e..1331ba49 100644
--- a/gcc/ipa-sra.cc
+++ b/gcc/ipa-sra.cc
@@ -2242,7 +2242,11 @@ isra_analyze_call (cgraph_edge *cs)
 	  BITMAP_FREE (analyzed);
 	}
     }
-  else
+  /* Don't set m_return_ignored for musttail calls.  The tailc/musttail passes
+     compare the returned value against the IPA-VRP return value range if
+     it is a singleton, but if the call is changed to something which doesn't
+     return anything, it will always fail.  */
+  else if (!gimple_call_must_tail_p (call_stmt))
     csum->m_return_ignored = true;
 }
 
diff --git a/gcc/testsuite/c-c++-common/pr119484.c b/gcc/testsuite/c-c++-common/pr119484.c
new file mode 100644
index 0000000..6ae7c9a
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/pr119484.c
@@ -0,0 +1,21 @@
+/* PR ipa/119484 */
+/* { dg-do compile { target musttail } } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+/* { dg-final { scan-tree-dump-times "bar\[.a-z0-9]* \\\(\[^\n\r]*\\\); \\\[tail call\\\] \\\[must tail call\\\]" 1 "optimized" } } */
+
+void foo (int);
+
+[[gnu::noinline]] static int
+bar (int x)
+{
+  foo (x);
+  return 0;
+}
+
+int
+baz (int x)
+{
+  if (x == 1)
+    [[gnu::musttail]] return bar (x);
+  return 0;
+}