https://bugs.llvm.org/show_bug.cgi?id=39685
Bug ID: 39685
Summary: Inserting an element to an undef vector
Product: libraries
Version: trunk
Hardware: All
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Backend: WebAssembly
Assignee: unassignedb...@nondot.org
Reporter: ahee...@gmail.com
CC: llvm-bugs@lists.llvm.org
```
target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
target triple = "wasm32-unknown-unknown"
define <16 x i8> @test(i8 %x) {
%v = insertelement <16 x i8> undef, i8 %x, i32 0
ret <16 x i8> %v
}
```
If you compile the code above with the command
llc -asm-verbose=false -wasm-keep-registers -wasm-disable-explicit-locals
-mattr=+simd128,+sign-ext test.ll
The result will be like
```
splat_v16i8:
.param i32
.result v128
i8x16.splat $push0=, $0
i8x16.replace_lane $push1=, $pop0, 1, $0
i8x16.replace_lane $push2=, $pop1, 2, $0
i8x16.replace_lane $push3=, $pop2, 3, $0
i8x16.replace_lane $push4=, $pop3, 4, $0
i8x16.replace_lane $push5=, $pop4, 5, $0
i8x16.replace_lane $push6=, $pop5, 6, $0
i8x16.replace_lane $push7=, $pop6, 7, $0
i8x16.replace_lane $push8=, $pop7, 8, $0
i8x16.replace_lane $push9=, $pop8, 9, $0
i8x16.replace_lane $push10=, $pop9, 10, $0
i8x16.replace_lane $push11=, $pop10, 11, $0
i8x16.replace_lane $push12=, $pop11, 12, $0
i8x16.replace_lane $push13=, $pop12, 13, $0
i8x16.replace_lane $push14=, $pop13, 14, $0
i8x16.replace_lane $push15=, $pop14, 15, $0
end_function
```
What does wasm backend do for undef elements? Does it initialize them to zero?
But anyway here, doesn't the first instruction, splat, set all elements to the
value give by the argument? I'm not sure why all 'replace_lane's below try to
set each element one by one with the same value, which was supposed to be done
anyway by the first splat instruction.
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