| Issue |
98223
|
| Summary |
clang generating compare-branch for a large switch statement
|
| Labels |
clang
|
| Assignees |
|
| Reporter |
appujee
|
It makes sense for a couple of cases but this one has a dozen case statements and I wonder why clang assumes that jump table is better?
```cpp
#include<cstring>
#include<wctype.h>
enum {
WC_TYPE_INVALID = 0,
WC_TYPE_ALNUM,
WC_TYPE_ALPHA,
WC_TYPE_BLANK,
WC_TYPE_CNTRL,
WC_TYPE_DIGIT,
WC_TYPE_GRAPH,
WC_TYPE_LOWER,
WC_TYPE_PRINT,
WC_TYPE_PUNCT,
WC_TYPE_SPACE,
WC_TYPE_UPPER,
WC_TYPE_XDIGIT,
WC_TYPE_MAX
};
int iswctype(wint_t wc, wctype_t char_class) {
switch (char_class) {
case WC_TYPE_ALNUM: return iswalnum(wc);
case WC_TYPE_ALPHA: return iswalpha(wc);
case WC_TYPE_BLANK: return iswblank(wc);
case WC_TYPE_CNTRL: return iswcntrl(wc);
case WC_TYPE_DIGIT: return iswdigit(wc);
case WC_TYPE_GRAPH: return iswgraph(wc);
case WC_TYPE_LOWER: return iswlower(wc);
case WC_TYPE_PRINT: return iswprint(wc);
case WC_TYPE_PUNCT: return iswpunct(wc);
case WC_TYPE_SPACE: return iswspace(wc);
case WC_TYPE_UPPER: return iswupper(wc);
case WC_TYPE_XDIGIT: return iswxdigit(wc);
default: return 0;
}
}
```
https://godbolt.org/z/jzx33W9Mx
```asm
iswctype: // @iswctype
cmp x1, #6
b.gt .LBB0_6
cmp x1, #3
b.gt .LBB0_11
cmp x1, #1
b.eq .LBB0_19
cmp x1, #2
b.eq .LBB0_23
cmp x1, #3
b.ne .LBB0_27
b iswblank
.LBB0_6:
cmp x1, #9
b.gt .LBB0_15
cmp x1, #7
b.eq .LBB0_20
cmp x1, #8
b.eq .LBB0_24
cmp x1, #9
b.ne .LBB0_27
b iswpunct
.LBB0_11:
cmp x1, #4
b.eq .LBB0_21
cmp x1, #5
b.eq .LBB0_25
cmp x1, #6
b.ne .LBB0_27
b iswgraph
.LBB0_15:
cmp x1, #10
b.eq .LBB0_22
cmp x1, #11
b.eq .LBB0_26
cmp x1, #12
b.ne .LBB0_27
b iswxdigit
.LBB0_19:
b iswalnum
.LBB0_20:
b iswlower
.LBB0_21:
b iswcntrl
.LBB0_22:
b iswspace
.LBB0_23:
b iswalpha
.LBB0_24:
b iswprint
.LBB0_25:
b iswdigit
.LBB0_26:
b iswupper
.LBB0_27:
mov w0, wzr
ret
```
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