[llvm] ConstraintElim: add dry-run routine to fail early (PR #99670)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

I managed to get access to a copy of SPEC2006. I'm happy to report that there are no binary changes, and that the compile time has improved by 0.9%, as measured with perf.

```
Program                                       compile_time
                                              baseline     patch   diff
External/SPEC/CFP2006/470.lbm/470.lbm            6.70         6.94  3.5%
External/SPEC/CFP2006/444.namd/444.namd        277.31       279.18  0.7%
External/S.../CFP2006/453.povray/453.povray    737.11       741.86  0.6%
External/S...NT2006/471.omnetpp/471.omnetpp   2325.30      2340.06  0.6%
External/SPEC/CFP2006/433.milc/433.milc        153.72       154.29  0.4%
External/S...C/CINT2006/445.gobmk/445.gobmk    897.01       899.44  0.3%
Bitcode/Be...hmarks/Halide/blur/halide_blur      1.43         1.43  0.0%
External/S...FP2006/482.sphinx3/482.sphinx3     98.46        98.14 -0.3%
External/S...06/483.xalancbmk/483.xalancbmk   7426.60      7397.76 -0.4%
External/S...C/CINT2006/456.hmmer/456.hmmer    339.66       337.53 -0.6%
External/S...NT2006/464.h264ref/464.h264ref    841.65       836.31 -0.6%
External/S...C/CINT2006/401.bzip2/401.bzip2     98.84        98.13 -0.7%
External/SPEC/CINT2006/403.gcc/403.gcc        2470.16      2442.94 -1.1%
External/S...C/CINT2006/473.astar/473.astar     72.93        72.03 -1.2%
External/S.../CFP2006/450.soplex/450.soplex    775.14       759.94 -2.0%
                           Geomean difference                      -0.9%
```

https://github.com/llvm/llvm-project/pull/99670