search for: _with_overflow

> If we don't care about trying to optimize out overflow checks in > InstCombine, I'd go with moving the complexity to CGP. I think instcombine should optimize out overflow checks (as it does today) without introducing _with_overflow calls. Are there reasons why such an approach would not work? > However, I think > InstCombine is doing the right thing here by forming these. I don't quite agree with you on this -- by materializing these intrinsics InstCombine is making every pass that runs after it less effective....

I've run into cases where, because not all of LLVM's optimizations understand the semantics of the `llvm.$op.with.overflow` intrinsics, canonicalizing compares to `llvm.$op.with.overflow` ends up preventing optimization. For instance, running the following snippet through `opt -indvars` optimizes `%to.optimize` to `true`, but running it through `opt -instcombine -indvars` does not. ```

Hi, The attached patch implements sub.ovf/mul.ovf intrinsics similarly to the recently added add.ovf intrinsics. These are useful for implementing some vm instructions like sub.ovf/mul.ovf in .NET IL efficiently. sub.ovf is supported in target independent lowering and on x86, while mul.ovf is only supported in the x86 backend. Please review