| Issue |
114734
|
| Summary |
[InstCombine] wrong folding of multiplication to shift for an undefined input
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
bongjunj
|
https://github.com/llvm/llvm-project/blob/390300d9f41df6ad71f0f4196ef4885d4bd5dc48/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp#L1769-L1783
Alive2 report: https://alive2.llvm.org/ce/z/qqQmaw
```llvm
----------------------------------------
define i32 @ashr_mul_times_3_div_2_exact_2.2(i32 %x) {
#0:
%#1 = sdiv i32 %x, 65535
%mul = mul nsw i32 %#1, 3
%ashr = ashr i32 %mul, 1
ret i32 %ashr
}
=>
define i32 @ashr_mul_times_3_div_2_exact_2.2(i32 %x) {
#0:
%#1 = sdiv i32 %x, 65535
%#2 = ashr i32 %#1, 1
%ashr = add nsw i32 %#1, %#2
ret i32 %ashr
}
Transformation doesn't verify!
ERROR: Value mismatch
Example:
i32 %x = undef
Source:
i32 %#1 = #x00000000 (0) [based on undef value]
i32 %mul = #x00000000 (0)
i32 %ashr = #x00000000 (0)
Target:
i32 %#1 = #x00000000 (0)
i32 %#2 = #x00000000 (0)
i32 %ashr = #x00000080 (128)
Source value: #x00000000 (0)
Target value: #x00000080 (128)
Summary:
0 correct transformations
1 incorrect transformations
0 failed-to-prove transformations
0 Alive2 errors
```
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