[llvm-bugs] [Bug 30543] New: 4.0 Regression in llvm.powi.f64 lowering on ARM

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=30543

            Bug ID: 30543
           Summary: 4.0 Regression in llvm.powi.f64 lowering on ARM
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: ARM
          Assignee: unassignedbugs at nondot.org
          Reporter: yyc1992 at gmail.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Compiling the following IR on arm

```
target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
target triple = "armv7l-unknown-linux-gnueabihf"

@.str = private unnamed_addr constant [4 x i8] c"%f\0A\00", align 1

; Function Attrs: noinline norecurse nounwind readnone
define double @f(double, i32) #0 {
top:
  %2 = tail call double @llvm.powi.f64(double %0, i32 %1)
  ret double %2
}

; Function Attrs: nounwind readnone
declare double @llvm.powi.f64(double, i32)

; Function Attrs: nounwind
define i32 @main() {
  %1 = tail call double @f(double 2.000000e+00, i32 62)
  %2 = tail call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([4 x i8],
[4 x i8]* @.str, i32 0, i32 0), double %1)
  ret i32 0
}

; Function Attrs: nounwind
declare i32 @printf(i8* nocapture readonly, ...)

attributes #0 = { noinline }
```

prints 2.0 instead of what 2^62 should be.

This is a regression in llvm 4.0 and is causing a lot of test failures in
julia.

Difference in the assembly

```
-       .save   {r11, lr}
-       push    {r11, lr}
-       mov     r2, r0
-       vmov    r0, r1, d0
-       bl      __powidf2
-       vmov    d0, r0, r1
-       pop     {r11, pc}
+       b       __powidf2
```

GDB confirmed that the input value to `__powidf2` is wrong.

Currently bisecting.

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