Bug 9097 – Value range propagation to disable some array bound tests

A little test program: void main(string[] args) { size_t a = 6000 + args.length; int[200] array; array[a % 100] = 1; } ----------------------- Compiled with "dmd -O -inline": __Dmain: L0: sub ESP, 0338h mov ECX, 0C8h push EDI mov EAX, 0340h[ESP] add EAX, 01770h mov 0Ch[ESP], EAX xor EAX, EAX lea EDI, 01Ch[ESP] rep stosd mov EAX, 0Ch[ESP] mov ECX, 064h xor EDX, EDX div ECX cmp EDX, 0C8h mov 8[ESP], EDX jb L47 mov EAX, 4 call near ptr _D5test27__arrayZ L47: mov EDX, 8[ESP] xor EAX, EAX mov dword ptr 01Ch[EDX*4][ESP], 1 pop EDI add ESP, 0338h ret _D5test27__arrayZ: L0: push EAX mov ECX, offset FLAT:_D5test212__ModuleInfoZ push EAX push ECX call near ptr __d_array_bounds ----------------------- Compiled with "dmd -O -inline -release -noboundscheck": __Dmain: sub ESP, 0330h mov ECX, 0C8h push EDI mov EAX, 0338h[ESP] add EAX, 01770h mov 4[ESP], EAX xor EAX, EAX lea EDI, 014h[ESP] rep stosd mov EAX, 4[ESP] mov ECX, 064h xor EDX, EDX div ECX xor EAX, EAX mov dword ptr 014h[EDX*4][ESP], 1 pop EDI add ESP, 0330h ret ----------------------- Value range propagation is able to tell that the value of "a % 100" can't be outside the 0..200 bounds of the array, so there is no point in performing the bound test even in nonrelease mode.

Commits pushed to master at https://github.com/D-Programming-Language/dmd https://github.com/D-Programming-Language/dmd/commit/186acf411866c1950b215f58fd57c08e903f588c Fix Issue 9097 - Value range propagation to disable some array bound tests Do not emit bounds check code if the index is statically known to be within bounds https://github.com/D-Programming-Language/dmd/commit/fe9bb4aaad8b9aa132bd86d7a1168be12fec5981 Merge pull request #1493 from yebblies/issue9097 Fix Issue 9097 - Value range propagation to disable some array bound tests

In past dmd generated this with "dmd -O -inline -release -noboundscheck": __Dmain: sub ESP, 0330h mov ECX, 0C8h push EDI mov EAX, 0338h[ESP] add EAX, 01770h mov 4[ESP], EAX xor EAX, EAX lea EDI, 014h[ESP] rep stosd mov EAX, 4[ESP] mov ECX, 064h xor EDX, EDX div ECX xor EAX, EAX mov dword ptr 014h[EDX*4][ESP], 1 pop EDI add ESP, 0330h ret Now it generates this in both the optimized build and the less optimized build "dmd -O -inline" (beside removing the array bound tests, it also avoids the "div"): __Dmain: sub ESP, 0324h mov ECX, 0C8h push EDI mov EAX, 032Ch[ESP] add EAX, 01770h mov 0324h[ESP], EAX xor EAX, EAX lea EDI, 4[ESP] rep stosd mov ECX, 0324h[ESP] mov EAX, ECX mov EDX, 051EB851Fh mul EDX shr EDX, 5 imul EAX, EDX, 064h sub ECX, EAX xor EAX, EAX mov dword ptr 4[ECX*4][ESP], 1 pop EDI add ESP, 0324h ret