[llvm-bugs] [Bug 28097] New: Constant store not optimized out of the loop

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=28097

            Bug ID: 28097
           Summary: Constant store not optimized out of the loop
           Product: libraries
           Version: 3.8
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Loop Optimizer
          Assignee: unassignedbugs at nondot.org
          Reporter: yyc1992 at gmail.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

In the following IR, there are only one store and one load in the loop.
The store has a constant address and constant value and is always executed
before the load so it should be fine to move it outside the loop even if the
load and the store can alias. However, `opt` does not do this optimization at
any optimization level.

```
; ModuleID = 'c.ll'
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

; Function Attrs: norecurse nounwind
define double @julia_mysum_simd2_64926(double** nocapture %slot, i64 %len,
double* %ptr) #0 {
top:
  br label %if22

if22:                                             ; preds = %if22, %top
  %i = phi i64 [ %3, %if22 ], [ 0, %top ]
  %s.128 = phi double [ %2, %if22 ], [ 0.000000e+00, %top ]
  store double* %ptr, double** %slot, align 8, !tbaa !0,
!llvm.mem.parallel_loop_access !3
  %0 = getelementptr double, double* %ptr, i64 %i
  %1 = load double, double* %0, align 8, !llvm.mem.parallel_loop_access !3
  %2 = fadd fast double %1, %s.128
  %3 = add nuw nsw i64 %i, 1, !simd_loop !5
  %exitcond = icmp eq i64 %3, %len
  br i1 %exitcond, label %L18, label %if22, !llvm.loop !4

L18:                                              ; preds = %if22
  %.lcssa = phi double [ %2, %if22 ]
  ret double %.lcssa
}

attributes #0 = { norecurse nounwind }

!0 = !{!1, !1, i64 0}
!1 = !{!"jtbaa_gcframe", !2}
!2 = !{!"jtbaa"}
!3 = !{!4}
!4 = distinct !{!4}
!5 = !{}
```

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