http://llvm.org/bugs/show_bug.cgi?id=3598
Summary: [clang codegen perf] Don't pass _Complex with byval if
you can avoid it
Product: clang
Version: unspecified
Platform: PC
OS/Version: All
Status: NEW
Keywords: code-quality
Severity: normal
Priority: P2
Component: LLVM Codegen
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
clang codegens a call to cacos with byval, which pins an alloca to the stack:
_Complex double foo2(_Complex double x) {
return cacosl(x);
}
This causes us to compile this to:
_foo2:
subl $60, %esp
movsd 76(%esp), %xmm0
movsd 68(%esp), %xmm1
movsd %xmm1, 24(%esp)
movsd %xmm0, 32(%esp)
movl 36(%esp), %eax
movl %eax, 16(%esp)
movl 32(%esp), %eax
movl %eax, 12(%esp)
movl 28(%esp), %eax
movl %eax, 8(%esp)
movl 24(%esp), %eax
movl %eax, 4(%esp)
leal 40(%esp), %eax
movl %eax, (%esp)
call _cacos
subl $4, %esp
movsd 48(%esp), %xmm0
movsd 40(%esp), %xmm1
movl 64(%esp), %eax
movsd %xmm1, (%eax)
movsd %xmm0, 8(%eax)
addl $60, %esp
ret $4
llvm-gcc doesn't do this.
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