ARM, AArch64, X86: Check preserved registers for tail calls.

We can only perform a tail call to a callee that preserves all the
registers that the caller needs to preserve.

This situation happens with calling conventions like preserver_mostcc or
cxx_fast_tls. It was explicitely handled for fast_tls and failing for
preserve_most. This patch generalizes the check to any calling
convention.

Related to rdar://24207743

Differential Revision: http://reviews.llvm.org/D18680

llvm-svn: 265329

1 files changed, 22 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/ARM/cxx-tlscc.ll b/llvm/test/CodeGen/ARM/cxx-tlscc.ll
index 48cce4f01be..d49c61ab093 100644
--- a/llvm/test/CodeGen/ARM/cxx-tlscc.ll
+++ b/llvm/test/CodeGen/ARM/cxx-tlscc.ll
@@ -126,5 +126,27 @@ entry:
   ret void
 }
 
+declare void @somefunc()
+define cxx_fast_tlscc void @test_ccmismatch_notail() {
+; A tail call is not possible here because somefunc does not preserve enough
+; registers.
+; CHECK-LABEL: test_ccmismatch_notail:
+; CHECK-NOT: b _somefunc
+; CHECK: bl _somefunc
+  tail call void @somefunc()
+  ret void
+}
+
+declare cxx_fast_tlscc void @some_fast_tls_func()
+define void @test_ccmismatch_tail() {
+; We can perform a tail call here because some_fast_tls_func preserves all
+; necessary registers (and more).
+; CHECK-LABEL: test_ccmismatch_tail:
+; CHECK-NOT: bl _some_fast_tls_func
+; CHECK: b _some_fast_tls_func
+  tail call cxx_fast_tlscc void @some_fast_tls_func()
+  ret void
+}
+
 attributes #0 = { nounwind "no-frame-pointer-elim"="true" }
 attributes #1 = { nounwind }