Bug on llvm backend (llc) when the integer type is not power of 2?

Hi all,

When I run cmd ‘llc -mtriple=x86_64-linux -filetype=obj tmp.ll -o tmp.o’ and ‘g++ tmp.o -o exe’ on following llvm-ir, I’ll get wrong output.
Here ‘%r’ and ‘%zt’ should be 0x3FFFD, but output is 0xFFFFFD.

Is this a bug?
If it’s a bug, then how can I workaround this? (Any llc option can avoid this?)

Thanks a lot!
Fangqing
Xilinx Inc.

; ModuleID = ‘main7.bc’

source_filename = “main.cpp”

target datalayout = “e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128”

target triple = “x86_64-unknown-linux-gnu”

@.str = private unnamed_addr constant [9 x i8] c"adu: %d\0A\00", align 1

; Function Attrs: noinline norecurse optnone uwtable

define i32 @main() #0 {

entry:

%a = alloca i24, align 4

store i24 -3, i24* %a, align 4; 0xFFFFFD

%bc = bitcast i24* %a to i18*

%r = load i18, i18* %bc, align 4

%zt = zext i18 %r to i40; should be 0x3FFFD

;%or = or i40 %zt, 267386880

%call = call i32 (i8*, …) @printf(i8* getelementptr inbounds ([9 x i8], [9 x i8]* @.str, i32 0, i32 0), i18 %r)

%call2 = call i32 (i8*, …) @printf(i8* getelementptr inbounds ([9 x i8], [9 x i8]* @.str, i32 0, i32 0), i40 %zt)

;%call3 = call i32 (i8*, …) @printf(i8* getelementptr inbounds ([9 x i8], [9 x i8]* @.str, i32 0, i32 0), i40 %or)

ret i32 0

}

declare i32 @printf(i8*, …) #1

attributes #0 = { noinline norecurse optnone uwtable “correctly-rounded-divide-sqrt-fp-math”=“false” “disable-tail-calls”=“false” “frame-pointer”=“all” “less-precise-fpmad”=“false” “no-infs-fp-math”=“false” “no-jump-tables”=“false” “no-nans-fp-math”=“false” “no-signed-zeros-fp-math”=“false” “no-trapping-math”=“false” “stack-protector-buffer-size”=“8” “target-cpu”=“x86-64” “target-features”="+fxsr,+mmx,+sse,+sse2,+x87" “unsafe-fp-math”=“false” “use-soft-float”=“false” }

attributes #1 = { “correctly-rounded-divide-sqrt-fp-math”=“false” “disable-tail-calls”=“false” “frame-pointer”=“all” “less-precise-fpmad”=“false” “no-infs-fp-math”=“false” “no-nans-fp-math”=“false” “no-signed-zeros-fp-math”=“false” “no-trapping-math”=“false” “stack-protector-buffer-size”=“8” “target-cpu”=“x86-64” “target-features”="+fxsr,+mmx,+sse,+sse2,+x87" “unsafe-fp-math”=“false” “use-soft-float”=“false” }

!llvm.module.flags = !{!0}

!llvm.ident = !{!1}

!0 = !{i32 1, !“wchar_size”, i32 4}

!1 = !{!"clang version 7.0.0 "}

Per the LangRef for load. https://llvm.org/docs/LangRef.html#id208

“When loading a value of a type like i20 with a size that is not an integral number of bytes, the result is undefined if the value was not originally written using a store of the same type.”