[llvm-bugs] [Bug 28567] [IPRA] Reg Usage Info Collector too aggressive.

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=28567

Vivek Pandya <vivekvpandya at gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
                 CC|                            |vivekvpandya at gmail.com
         Resolution|INVALID                     |---

--- Comment #2 from Vivek Pandya <vivekvpandya at gmail.com> ---
I don't think current implement is correct because I have a very simple example
on X86 where only CL is clobbered than also CH is marked as clobbered :

target triple = "x86_64--"

define i8 @main(i8 %X) {
  %inc = add i8 %X, 1
  %inc2 = mul i8 %inc, 5
  ret i8 %inc2
}

for above llvm IR generated X86 code is as follow:

main:                                   # @main
    .cfi_startproc
# BB#0:
    movb    $5, %cl
    movl    %edi, %eax
    mulb    %cl
    addb    $5, %al
    retq

So here it is very clear that only CL, CX, RCX, ECX should be marked as
clobbered but current implementation marks CH too.

Here is review request https://reviews.llvm.org/D22400 that should fix this.

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