diff options
| author | cinap_lenrek <cinap_lenrek@felloff.net> | 2018-11-18 20:42:45 +0100 |
|---|---|---|
| committer | cinap_lenrek <cinap_lenrek@felloff.net> | 2018-11-18 20:42:45 +0100 |
| commit | 485a3301e6119f0c85d7869d469fc0a0888e49c1 (patch) | |
| tree | 7e79e11abf1349597d3226f8cef5a4493c413bf1 /sys/src/cmd/cc | |
| parent | b6251bff913972b5dfb421813fe97a5bfff3627f (diff) | |
cc: fix wrong "useless or misleading comparison" warning
to reproduce:
u8int x, y;
x = 0xff;
y = 0xc0;
if((s8int)(x & y) >= 0)
print("help\n");
compiles correctly but prints a warning
warning: test.c:11 useless or misleading comparison: UINT >= 0
the issue is that compar() unconditionally skipped over
all left casts ignoring the case when a cast would sign
extend the value.
the new code only skips over the cast when the original
type with is smaller than the cast result or when they
are equal width and types have same signedness. so the
effective left hand side type is the last truncation
or sign extension.
Diffstat (limited to 'sys/src/cmd/cc')
| -rw-r--r-- | sys/src/cmd/cc/com.c | 27 |
1 files changed, 17 insertions, 10 deletions
diff --git a/sys/src/cmd/cc/com.c b/sys/src/cmd/cc/com.c index b8a3b5c44..f67294510 100644 --- a/sys/src/cmd/cc/com.c +++ b/sys/src/cmd/cc/com.c @@ -1373,14 +1373,21 @@ compar(Node *n, int reverse) /* * Skip over left casts to find out the original expression range. */ - while(l->op == OCAST) + while(l->op == OCAST){ + lt = l->type; + rt = l->left->type; + if(lt == T || rt == T) + return 0; + if(lt->width < rt->width) + break; + if(lt->width == rt->width && ((lt->etype ^ rt->etype) & 1) != 0) + break; l = l->left; + } if(l->op == OCONST) return 0; lt = l->type; - if(lt == T) - return 0; - if(lt->etype == TXXX || lt->etype > TUVLONG) + if(lt == T || lt->etype == TXXX || lt->etype > TUVLONG) return 0; /* @@ -1399,16 +1406,17 @@ compar(Node *n, int reverse) if((rt->etype&1) && r->vconst < 0) /* signed negative */ x.a = ~0ULL; - if((lt->etype&1)==0){ + if(lt->etype & 1){ + /* signed */ + lo = big(~0ULL, -(1LL<<(lt->width*8-1))); + hi = big(0, (1LL<<(lt->width*8-1))-1); + } else { /* unsigned */ lo = big(0, 0); if(lt->width == 8) hi = big(0, ~0ULL); else - hi = big(0, (1LL<<(l->type->width*8))-1); - }else{ - lo = big(~0ULL, -(1LL<<(l->type->width*8-1))); - hi = big(0, (1LL<<(l->type->width*8-1))-1); + hi = big(0, (1LL<<(lt->width*8))-1); } switch(op){ @@ -1462,4 +1470,3 @@ if(debug['y']) prtree(n, "strange"); warn(n, "useless or misleading comparison: %s", cmpbuf); return 0; } - |