[llvm-bugs] [Bug 49162] New: Wrong code generated for code sequence shl/ashr/trunc/ashr

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=49162

            Bug ID: 49162
           Summary: Wrong code generated for code sequence
                    shl/ashr/trunc/ashr
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: carrot at google.com
                CC: craig.topper at gmail.com, llvm-bugs at lists.llvm.org,
                    llvm-dev at redking.me.uk, pengfei.wang at intel.com,
                    spatel+llvm at rotateright.com

This bug entry is requested by @RKSimon, trunc llvm generates wrong code for
the following test case

define i32* @PRXXXXXX(i32* %base, i160* %ptr160) {
  %load160 = load i160, i160* %ptr160, align 4
  %shl = shl i160 %load160, 80
  %ashr160 = ashr i160 %shl, 112
  %trunc = trunc i160 %ashr160 to i64
  %ashr64 = ashr i64 %trunc, 32
  %gep = getelementptr inbounds i32, i32* %base, i64 %ashr64
  ret i32* %gep
}

PRXXXXXX: # @PRXXXXXX
  lea rax, [rdi - 4]
  ret

Correct result should be

PRXXXXXX: # @PRXXXXXX
  mov eax, dword ptr [rsi + 8]
  shl eax, 16
  cdqe
  sar rax, 16
  lea rax, [rdi + 4*rax]
  ret

It is also demonstrated by https://godbolt.org/z/snajbG.

It is caused by patch
https://reviews.llvm.org/rG69bc0990a9181e6eb86228276d2f59435a7fae67.

-- 
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/20210212/3e00680b/attachment.html>