[Wasm R2R] Fix unsigned add/sub overflow codegen#129106
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genCodeForBinaryOverflow in codegenwasm.cpp was emitting the signed XOR-based overflow algorithm for GT_ADD and GT_SUB regardless of treeNode->IsUnsigned(). For add.ovf.un / sub.ovf.un the signed check only fires when the two operand sign bits match, so unsigned overflows where the operands have different high bits were silently wrapped without throwing OverflowException. Branch on IsUnsigned() in both cases. For unsigned add, overflow iff result < op1 (unsigned compare). For unsigned sub, overflow iff op1 < op2 (unsigned compare). The existing signed algorithm is preserved unchanged in the else branch. GT_MUL already had the same IsUnsigned()-based split, so the pattern is consistent with the rest of the function. Contributes to dotnet#128234. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Pull request overview
This PR corrects WASM-specific JIT codegen for overflow-checked GT_ADD/GT_SUB when the IR node is marked unsigned, by emitting unsigned overflow detection rather than the existing signed (XOR/sign-bit) algorithm. This aligns the generated Wasm for add.ovf.un / sub.ovf.un semantics and should address incorrect codegen in R2R scenarios.
Changes:
- Update overflow-checked
GT_ADDto use an unsigned compare (result < op1) to detect unsigned addition overflow. - Update overflow-checked
GT_SUBto use an unsigned compare (op1 < op2) to detect unsigned subtraction overflow. - Keep the existing signed overflow logic (XOR-based sign checks) for signed add/sub cases.
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genCodeForBinaryOverflow in codegenwasm.cpp was emitting the signed XOR-based overflow algorithm for GT_ADD and GT_SUB regardless of treeNode->IsUnsigned(). Fix this.
Contributes to #128234.