• d-bugmail puremagic.com (52/52) May 28 2022 https://issues.dlang.org/show_bug.cgi?id=23146

d-bugmail puremagic.com writes:

https://issues.dlang.org/show_bug.cgi?id=23146

          Issue ID: 23146
           Summary: bounds checking is still done in  system functions
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: regression
          Priority: P1
         Component: dmd
          Assignee: nobody puremagic.com
          Reporter: bugzilla digitalmars.com

Given:

 system int test(int[] a) { return a[3]; }

and compiling it with -vasm:

_D4testQfFAiZi:
0000:   55                       push      RBP
0001:   48 8B EC                 mov       RBP,RSP
0004:   48 83 EC 20              sub       RSP,020h
0008:   48 89 5D E8              mov       -018h[RBP],RBX
000c:   48 89 7D F0              mov       -010h[RBP],RDI
0010:   48 89 75 F8              mov       -8[RBP],RSI
0014:   B8 03 00 00 00           mov       EAX,3
0019:   48 3B F8                 cmp       RDI,RAX
001c:   77 15                    ja        L33
001e:   48 89 F9                 mov       RCX,RDI
0021:   48 89 C2                 mov       RDX,RAX
0024:   BE 07 00 00 00           mov       ESI,7
0029:   BF 00 00 00 00           mov       EDI,0
002e:   E8 00 00 00 00           call      L0
0033:   48 8B 55 F8              mov       RDX,-8[RBP]
0037:   48 8B 5D F0              mov       RBX,-010h[RBP]
003b:   8B 42 0C                 mov       EAX,0Ch[RDX]
003e:   48 8B 5D E8              mov       RBX,-018h[RBP]
0042:   C9                       leave
0043:   C3                       ret

as you can see, the bounds check is there. Now let's compile it with
-boundscheck=off:

0000:   55                       push      RBP
0001:   48 8B EC                 mov       RBP,RSP
0004:   48 83 EC 10              sub       RSP,010h
0008:   48 89 7D F0              mov       -010h[RBP],RDI
000c:   48 89 75 F8              mov       -8[RBP],RSI
0010:   48 8B 55 F8              mov       RDX,-8[RBP]
0014:   48 8B 45 F0              mov       RAX,-010h[RBP]
0018:   8B 42 0C                 mov       EAX,0Ch[RDX]
001b:   C9                       leave
001c:   C3                       ret

and no bounds check.

This bug was introduced by https://github.com/dlang/dmd/pull/14170

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