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2017 Mar 15
2
Speculative execution of FP divide Instructions - Call-Graph Simplify
Hi all,
I came across an issue caused by the Call-Graph Simplify Pass. Here is a a
small repro:
```
define double @foo(double %a1, double %a2, double %a3) #0 {
entry:
%a_mul = fmul double %a1, %a2
%a_cmp = fcmp ogt double %a3, %a_mul
br i1 %a_cmp, label %a.then, label %a.end
a.then:
%a_div = fdiv double %a_mul, %a3
br label %a.end
a.end:
%a_factor = phi double [ %a_div, %a.then ],
2017 Mar 15
3
Speculative execution of FP divide Instructions - Call-Graph Simplify
[+current llvm-dev address]
On 03/15/2017 09:23 AM, Hal Finkel wrote:
> Hi Samuel,
>
> What are you taking about? ;)
>
> The only way to get a SIGFPE from a floating-point division by zero is
> to modify the floating-point environment to enable those exceptions.
> We don't support that (*). In the default (supported) environment,
> floating point division is well
2017 Mar 15
2
Speculative execution of FP divide Instructions - Call-Graph Simplify
It’s true, I am working on this. I have committed the initial patch to add constrained intrinsics for the basic FP operations. This has the desired effect of preventing optimizations that would violate strict FP semantics with regard to rounding mode and exception status, but it also prevents many safe optimizations. Later this year I’ll be going through the code base and trying to teach