https://llvm.org/bugs/show_bug.cgi?id=31275
Bug ID: 31275
Summary: Binary rotation is not detected after multiplication
Product: clang
Version: unspecified
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: -New Bugs
Assignee: unassignedclangb...@nondot.org
Reporter: funny.fal...@gmail.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
I found that clang produces bad code for rotation after multiplication.
Although it generates good code, if multiplication is not last operation:
// Type your code here, or load an example.
#define rotl(x,n) (((x)<<(n))|((x)>>(32-(n))))
unsigned mult_rotl(unsigned num, unsigned mun) {
return rotl(num*9, 7);
}
unsigned mult_add_rotl(unsigned num, unsigned mun) {
return rotl(num*9+1, 7);
}
mult_rotl:
leal (%rdi,%rdi,8), %eax
shll $7, %edi
leal (%rdi,%rdi,8), %ecx
shrl $25, %eax
orl %ecx, %eax
retq
mult_add_rotl:
leal 1(%rdi,%rdi,8), %eax
roll $7, %eax
retq
(probably, it is llvm-optimizer's issue)
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