[llvm-bugs] [Bug 42062] New: tail call causes to run out of registers during register allocation

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=42062

            Bug ID: 42062
           Summary: tail call causes to run out of registers during
                    register allocation
           Product: libraries
           Version: trunk
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: ARM
          Assignee: diogo.sampaio at arm.com
          Reporter: diogo.sampaio at arm.com
                CC: llvm-bugs at lists.llvm.org, peter.smith at linaro.org,
                    Ties.Stuij at arm.com

llc in the code:
--
target triple = "thumbv8m.base-arm-none-eabi"
@foo = external global i8
declare i32 @bar(i8* nocapture, i32, i32, i8* nocapture) 

define void @food(i8* %a) #0 {
entry:
  %0 = tail call i32 @bar(i8* %a, i32 8, i32 1, i8* nonnull @foo)
  %1 = tail call i32 @bar(i8* %a, i32 9, i32 0, i8* nonnull @foo)
  %2 = tail call i32 @bar(i8* %a, i32 7, i32 2, i8* nonnull @foo)
  ret void
}
attributes #0 = { minsize "target-cpu"="cortex-m23" }
--
will produce an error: ran out of registers during register allocation

running --disable-tail-calls won't

In thumb there are only 8 registers. In this particular case, the register
allocator could move the bar address, stored in r6 to register r7 and allow the
register r4, r5, r6 to be restored. But he does not.

-- 
You are receiving this mail because:
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-bugs/attachments/20190529/e9998cc6/attachment.html>