[llvm-dev] Signed or unsigned EQ/NEQ (original) (raw)

Dounia Khaldi via llvm-dev llvm-dev at lists.llvm.org
Mon Nov 20 08:36:53 PST 2017

Thanks, James. This answers my question. I will have to retrieve other operations that use the same value. But even this won't work in all case.

On Sat, Nov 18, 2017 at 7:28 AM, James Courtier-Dutton < james.dutton at gmail.com> wrote:

Hi,

I am writing a decompiler. For this, i need to do type inference propagation. EQ/NEQ do not provide any indication of type. So the only solution is to infer it from other uses of the same registers. I think you will have to do the same. Also, there are problem edge cases. What if one register is signed and the other is unsigned? Kind regards James On 17 Nov 2017 21:12, "Dounia Khaldi via llvm-dev" <_ _llvm-dev at lists.llvm.org> wrote:

Hello,

In one of the loop transformations I am developing, I need to convert eq and neq loop latch condition into less than or greater than depending on the control flow.

The problem is that CmpInst::ICMPEQ and CmpInst::ICMPNE are neither signed nor unsigned in LLVM. Also, I did not find a way to find out if the integer operands of the CmpInst are signed or unsigned. Apparently, LLVM does not distinguish in its type system between signed and unsigned variables. So, I am not able to generate the appropriate signed or unsigned ICMP(S|U)LT or ICMP(S|U)GT. Do you have a solution for this? Thanks, Dounia

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