https://bugs.llvm.org/show_bug.cgi?id=35745
Bug ID: 35745
Summary: Ignoring to directly use EAX register while preserving
it for the same return value
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: X86
Assignee: unassignedb...@nondot.org
Reporter: mrrr...@gmail.com
CC: llvm-bugs@lists.llvm.org
Created attachment 19602
--> https://bugs.llvm.org/attachment.cgi?id=19602&action=edit
Same testcase as on god bolt link
Here is the god bolt link with the short testcase https://godbolt.org/g/KZCFUC
struct mrgl_hashmap_node* pNode = pMainNode->pNext;
while(pNode != NULL){
if(pNode->key == key){
return pNode;
}
pNode = pNode->pNext;
}
return pNode;
mov edx, dword ptr [edx + esi + 12]
xor eax, eax
test edx, edx
jne .LBB0_3
jmp .LBB0_5
.LBB0_6: # in Loop: Header=BB0_3 Depth=1
mov edx, dword ptr [edx + 4]
test edx, edx
je .LBB0_5
.LBB0_3: # =>This Inner Loop Header: Depth=1
cmp dword ptr [edx], ecx
jne .LBB0_6
mov eax, edx
.LBB0_5:
pop esi
ret
Instead of loading pointer in edx, codegen could use eax directly so we will
not need to "xor eax, eax" and "mov eax, edx" which is clang did perfectly with
previous if statement (row 44) in test case where is mask used directly as
return result. Gcc 7.2.0 does perfect job with it and use eax directly.
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