clang optimizes tail calls, as in this example:
int foo(void);
int bar(void) {
return foo();
}
where the call is transformed to:
calll .L0$pb
.L0$pb:
popl %eax
.Ltmp0:
addl $_GLOBAL_OFFSET_TABLE_+(.Ltmp0-.L0$pb), %eax
movl foo@GOT(%eax), %eax
popl %ebp
jmpl *%eax # TAILCALL
However, the GOT references must all be resolved at dlopen() time, and so this
approach cannot be used with lazy dynamic linking (e.g. using RTLD_LAZY), which
usually populates the PLT with stubs that perform the actual resolving.
This patch changes X86TargetLowering::LowerCall() to skip tail call
optimization, if the called function is a global or external symbol.
Patch by Dimitry Andric!
PR15086
llvm-svn: 195318
This reverts commit 8b75e6bc35fb3f9c1e788dbd05084c0f4a60a0f3.
The FileCheck tests are not equivalent:
test/CodeGen/X86/tailcall-structret.ll:6:10: error: expected string not found in input
; CHECK: jmp init
^
<stdin>:1:2: note: scanning from here
.section __TEXT,__text,regular,pure_instructions
^
<stdin>:13:2: note: possible intended match here
jmp _init ## TAILCALL
^
llvm-svn: 175124
enabled by passing -tailcallopt to llc. The optimization is
performed if the following conditions are satisfied:
* caller/callee are fastcc
* elf/pic is disabled OR
elf/pic enabled + callee is in module + callee has
visibility protected or hidden
llvm-svn: 42870
