[compiler-rt] compiler-rt/arm: Check for overflow when adding float denorms (PR #185245)

[Peter Smith via llvm-commits]

smithp35 wrote:

First thought is that we should add a test. I'm thinking something like https://github.com/llvm/llvm-project/blob/main/compiler-rt/test/builtins/Unit/mulsf3_test.c 

Although I don't think it is the responsibility of this PR to add a full test suite for addsf3, it can just add the test for checking overflow when adding float denorms.

Getting the tests to run on an Arm machine in soft-float may be a bit of a faff. It needs compiler-rt built with tests enabled and a way of executing the tests. I expect that running qemu user mode arm emulation with a sysroot from the soft-float arm-linux-gnueabi toolchain would work.

Some years ago I wrote that up in https://llvm.org/docs/HowToCrossCompileBuiltinsOnArm.html although I am not sure how up to date that is with a more modern compiler-rt 

https://github.com/llvm/llvm-project/pull/185245