https://llvm.org/bugs/show_bug.cgi?id=26327
Bug ID: 26327
Summary: [x86] Redundant displacement in calls to virtual base
class function with this-adjustment
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: Backend: X86
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Blocks: 26299
Classification: Unclassified
Consider:
struct Base1 { virtual void f1(); };
struct Base2 { virtual void f2(); };
struct S : Base1, Base2 {
void foo();
};
void S::foo() {
f2();
}
At -Os, we generate:
00000000 <?foo@S@@QAEXXZ>:
0: 8b 41 04 mov 0x4(%ecx),%eax
3: 83 c1 04 add $0x4,%ecx
6: ff 20 jmp *(%eax)
MSVC generates:
?foo@S@@QAEXXZ (public: void __thiscall S::foo(void)):
00000000: 83 C1 04 add ecx,4
00000003: 8B 01 mov eax,dword ptr [ecx]
00000005: FF 20 jmp dword ptr [eax]
saving one byte, admittedly at the cost of a longer dependency chain. Maybe
that's worth it at -Os though?
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