https://llvm.org/bugs/show_bug.cgi?id=31667
Bug ID: 31667
Summary: inefficient code for i16 bit
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Backend: X86
Assignee: asaf.bad...@intel.com
Reporter: asaf.bad...@intel.com
CC: amjad.ab...@intel.com, llvm-bugs@lists.llvm.org
Classification: Unclassified
Given:
define i16 @test(i16 %data) {
entry:
%shr1 = lshr i16 %data, 1
%shr1.1 = lshr i16 %data, 3
%ret = sub i16 %shr1.1, %shr1
ret i16 %ret
}
Generated asm:
movl %ecx, %eax
andl $65528, %eax # imm = 0xFFF8
andl $65534, %ecx # imm = 0xFFFE
shrl %ecx
shrl $3, %eax
subl %ecx, %eax
retq
The optimal expected asm:
andl $65535, %eax # imm = 0xFFFF
movl %eax, %ecx
shrl %ecx
shrl $3, %eax
subl %ecx, %eax
retq
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