https://llvm.org/bugs/show_bug.cgi?id=30644
Bug ID: 30644
Summary: ROTATE by 1 instruction is preferable over ROTATE with
immediate
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: Backend: X86
Assignee: unassignedb...@nondot.org
Reporter: zvi.racko...@intel.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
For the following test
define i32 @rotr1_32(i32 %A) {
%B = shl i32 %A, 31
%C = lshr i32 %A, 1
%D = or i32 %B, %C
ret i32 %D
}
We generate:
roll $31, %eax
It would be better to generate:
rorl $eax
Rotate by 1 is translated to 1 micro-op, while rotate with imm8 is translated
to 2 micro-ops.
We appear to select to ROL1 instructions, but not the ROR1 instructions.
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