https://bugs.llvm.org/show_bug.cgi?id=48909
Bug ID: 48909
Summary: Missed optimization: llvm unable to remove bounds
check
Product: new-bugs
Version: unspecified
Hardware: PC
OS: All
Status: NEW
Severity: enhancement
Priority: P
Component: new bugs
Assignee: unassignedb...@nondot.org
Reporter: alex.gay...@gmail.com
CC: htmldevelo...@gmail.com, llvm-bugs@lists.llvm.org
https://godbolt.org/z/vEfPYj (also below)
LLVM should be able to remove the branch that leads to the call to abort() --
data.length is known to be the same as block_len, and block_len is known not to
be 0. Therefore llvm should know that block_len - is always < data.length.
Source:
#include <stdlib.h>
#include <stdbool.h>
#include <stdint.h>
typedef struct {
uint8_t *data;
size_t length;
} slice;
static inline uint8_t subscript(slice data, size_t index) {
if (index >= data.length) {
abort();
}
return data.data[index];
}
bool check_padding(slice data, size_t block_len) {
if (data.length != block_len || block_len == 0) {
return false;
}
uint8_t pad_size = subscript(data, block_len - 1);
return pad_size > 7;
}
generated assembly:
check_padding: # @check_padding
push rax
xor eax, eax
cmp rsi, rdx
jne .LBB0_4
test rdx, rdx
je .LBB0_4
test rsi, rsi
je .LBB0_5
cmp byte ptr [rsi + rdi - 1], 7
seta al
.LBB0_4:
pop rcx
ret
.LBB0_5:
call abort
--
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