| Issue |
74326
|
| Summary |
InstCombine: fold of shuffle into fadd changes NaN payload
|
| Labels |
miscompilation,
llvm:instcombine,
floating-point
|
| Assignees |
|
| Reporter |
nunoplopes
|
This optimization changes the NaN payload. Originally it was a pass-through for the last 2 elements, while the optimized code can produce more NaN payloads.
```llvm
; llvm/test/Transforms/InstCombine/shuffle_select-inseltpoison.ll
define <4 x float> @fadd(<4 x float> %v) {
%b = fadd <4 x float> %v, { 41.000000, 42.000000, 43.000000, 44.000000 }
%s = shufflevector <4 x float> %b, <4 x float> %v, 0, 1, 6, 7
ret <4 x float> %s
}
=>
define <4 x float> @fadd(<4 x float> %v) {
%s = fadd <4 x float> %v, { 41.000000, 42.000000, -0.000000, -0.000000 }
ret <4 x float> %s
}
Transformation doesn't verify!
ERROR: Value mismatch
Example:
<4 x float> %v = < #xff800400 (SNaN), #x00000000 (+0.0), #x7f804000 (SNaN), #x00000000 (+0.0) >
Source:
<4 x float> %b = < #x7f800400 (SNaN), #x42280000 (42), #x7f804000 (SNaN), #x42300000 (44) >
<4 x float> %s = < #x7f800400 (SNaN), #x42280000 (42), #x7f804000 (SNaN), #x00000000 (+0.0) >
Target:
<4 x float> %s = < #xff800400 (SNaN), #x42280000 (42), #xff804000 (SNaN), #x00000000 (+0.0) >
Source value: < #x7f800400 (SNaN), #x42280000 (42), #x7f804000 (SNaN), #x00000000 (+0.0) >
Target value: < #xff800400 (SNaN), #x42280000 (42), #xff804000 (SNaN), #x00000000 (+0.0) >
```
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