Emit error on array size overflow

[P-E-P]

When the byte size required for an array overflow we should emit an error.

Fixes #3962

[philberty]

Nice one didnt know you can do that

[philberty]

looks like there is a regression here on running on 32 bit platforms. So this __builtin wont work.

Its definetlyy worth checking this in C/C++ on compiler explorer and if they make the same error and work back from that error message.

[philberty]

I think your Fix is partly right there are two parts to fix this properly.

1. Overflow check the value
2. Add a MAX alloc limit of 2gb i think is what rustc does from reading it ages ago.

So 1,

I think you need to add a check like you have or you could put it into typechecking over in

gccrs/gcc/rust/typecheck/rust-hir-type-check-expr.cc

Line 1153 in b7c9aaa

tree capacity_value

But maybe its enough to leave it wher you have it.

You should be able to do:

if (TREE_OVERFLOW_P (capacity_expr)) 
{
}

We track the capacity expr as part of the Array type now.

PArt 2: detect the HUGE array

tree len = capacity_expr
tree esize = TYPE_SIZE_UNIT (elt_type);     // bytes, INTEGER_CST
tree bytes = fold_build2 (MULT_EXPR, sizetype,
                          fold_convert (sizetype, len),
                          fold_convert (sizetype, esize));

if (TREE_OVERFLOW_P (bytes)) 

Or also put in a new constant for 2gb maybe make it a new option in lang.opts so it can be changed but it defaults to 2gb as the final check.

I think should do this.

[philberty]

I added some suggestions to try in the comments

[philberty]

Also debug_tree is super useful here

[philberty]

I think this is a good sign your getting:

Executing on host: /home/runner/work/gccrs/gccrs/gccrs-build/gcc/testsuite/rust/../../gccrs -B/home/runner/work/gccrs/gccrs/gccrs-build/gcc/testsuite/rust/../../  /home/runner/work/gccrs/gccrs/gcc/testsuite/rust/compile/issue-3962.rs  -m32  -fdiagnostics-plain-output   -frust-incomplete-and-experimental-compiler-do-not-use   -S -o issue-3962.s    (timeout = 300)
spawn -ignore SIGHUP /home/runner/work/gccrs/gccrs/gccrs-build/gcc/testsuite/rust/../../gccrs -B/home/runner/work/gccrs/gccrs/gccrs-build/gcc/testsuite/rust/../../ /home/runner/work/gccrs/gccrs/gcc/testsuite/rust/compile/issue-3962.rs -m32 -fdiagnostics-plain-output -frust-incomplete-and-experimental-compiler-do-not-use -S -o issue-3962.s
/home/runner/work/gccrs/gccrs/gcc/testsuite/rust/compile/issue-3962.rs:2:19: error: left shift count >= width of type
compiler exited with status 1
FAIL: rust/compile/issue-3962.rs  at line 3 (test for errors, line 2)
FAIL: rust/compile/issue-3962.rs (test for excess errors)
Excess errors:
/home/runner/work/gccrs/gccrs/gcc/testsuite/rust/compile/issue-3962.rs:2:19: error: left shift count >= width of type

[philberty]

not100% sure whats the best way to add tests for errors on m32 vs m64 here @dkm might know better

[P-E-P]

2. Add a MAX alloc limit of 2gb i think is what rustc does from reading it ages ago.

Or also put in a new constant for 2gb maybe make it a new option in lang.opts so it can be changed but it defaults to 2gb as the final check.

Are you sure about that ?

https://godbolt.org/z/Mr684qqsT

rustc does not throw an error message when the allocation is too big.

EDIT: It does since rustc 1.55 although I can't find anything about a 2Gb limit.