<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/100661>100661</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            IPSCCP pass wrong denormal constant optimization
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          hashemthomas1
      </td>
    </tr>
</table>

<pre>
    Hi,

I work on a target that supports denormal-fp-math=preserve-sign,preserve-sign mode and I've encountered the following bug:
https://godbolt.org/z/Tj78Y63KM

In the link I'm using x86 top of trunk compiler with the addition of the command line flag: 
-fdenormal-fp-math=preserve-sign,preserve-sign

As you can see, a wrong constant propagation happens as one of the operands is a denormal.
The output of the optimized function is a denormal when it's supposed to be 0.0f.

After debugging, I found out that the bug happens in IPSCCP pass when it tries to simplify a binary operation.
More specifically, in (/llvm-project/llvm/lib/Transforms/Utils/SCCPSolver.cpp):
```
void SCCPInstVisitor::visitBinaryOperator(Instruction &I)
```

The following line:
```
Value *R = simplifyBinOp(I.getOpcode(), V1, V2, SimplifyQuery(DL));
```
Initializes a SimplifyQuery instance  without a context, which results in a chain of function calls reaching the function
(/llvm-project/llvm/lib/Analysis/InstructionSimplify.cpp):
```
static Constant *foldOrCommuteConstant(Instruction::BinaryOps Opcode,
 Value *&Op0, Value *&Op1,
 const SimplifyQuery &Q)
```

In case a context is **not** given, the function:
```
ConstantFoldBinaryOpOperands(Opcode, CLHS, CRHS, Q.DL);
```
and doesn't flush inputs to zero when needed.

Otherwise, if a context **is** given the function:
```
ConstantFoldFPInstOperands(Opcode, CLHS, CRHS, Q.DL, Q.CxtI);
```
is called instead, performing a correct constant fold that flushes inputs to zero.

Therefore, the solution would be to pass the context to the SimplifyQuery initialization in (/llvm-project/llvm/lib/Transforms/Utils/SCCPSolver.cpp):
```
Value *R = simplifyBinOp(I.getOpcode(), V1, V2, SimplifyQuery(DL, &I));
```

Note that even though EarlyCSE also calls the function SimplifyInstruction, 
we don't encounter this bug because the SimplifyQuery instance is initialized with context.

</pre>
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