[llvm-bugs] [Bug 47812] New: CTR not correctly saved for inline assembly clobbering CTR

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=47812

            Bug ID: 47812
           Summary: CTR not correctly saved for inline assembly clobbering
                    CTR
           Product: libraries
           Version: 11.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: PowerPC
          Assignee: unassignedbugs at nondot.org
          Reporter: programmerjake at gmail.com
                CC: llvm-bugs at lists.llvm.org, nemanja.i.ibm at gmail.com

The following IR is miscompiled:
https://gcc.godbolt.org/z/s5zcae

target triple = "powerpc64le-unknown-linux-gnu"

define void @f(void()* %fn) {
  call void asm sideeffect "mtctr 31", "~{ctr}"()
  tail call void %fn()
  ret void
}

Generated Assembly (trimmed to just f's instructions, comments added):
f:
.Lfunc_gep0:
        addis 2, 12, .TOC.-.Lfunc_gep0 at ha
        addi 2, 2, .TOC.-.Lfunc_gep0 at l
        mflr 0
        std 0, 16(1)
        stdu 1, -32(1)
        std 2, 24(1)
        mtctr 3
        mr      12, 3
        mtctr   31 # note how ctr not restored before the call on next line
        bctrl
        ld 2, 24(1)
        addi 1, 1, 32
        ld 0, 16(1)
        mtlr 0
        blr

This causes f to call whatever address was in r31 instead of %fn despite the
inline assembly including ctr in the clobber list.

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