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Fold divisions by 0. (#1963)
The current implementation in the folder when seeing a division by zero is to assert. In the release build, the compiler will attempt to compute the value, which causes its own problems. The solution I will go with is to fold the division, and just give it the value of 0. The same goes for remainder and mod operations. Fixes #1961.
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@ -69,29 +69,49 @@ uint32_t InstructionFolder::BinaryOperate(SpvOp opcode, uint32_t a,
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case SpvOp::SpvOpIMul:
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return a * b;
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case SpvOp::SpvOpUDiv:
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assert(b != 0);
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return a / b;
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if (b != 0) {
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return a / b;
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} else {
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// Dividing by 0 is undefined, so we will just pick 0.
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return 0;
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}
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case SpvOp::SpvOpSDiv:
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assert(b != 0u);
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return (static_cast<int32_t>(a)) / (static_cast<int32_t>(b));
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if (b != 0u) {
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return (static_cast<int32_t>(a)) / (static_cast<int32_t>(b));
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} else {
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// Dividing by 0 is undefined, so we will just pick 0.
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return 0;
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}
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case SpvOp::SpvOpSRem: {
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// The sign of non-zero result comes from the first operand: a. This is
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// guaranteed by C++11 rules for integer division operator. The division
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// result is rounded toward zero, so the result of '%' has the sign of
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// the first operand.
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assert(b != 0u);
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return static_cast<int32_t>(a) % static_cast<int32_t>(b);
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if (b != 0u) {
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return static_cast<int32_t>(a) % static_cast<int32_t>(b);
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} else {
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// Remainder when dividing with 0 is undefined, so we will just pick 0.
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return 0;
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}
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}
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case SpvOp::SpvOpSMod: {
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// The sign of non-zero result comes from the second operand: b
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assert(b != 0u);
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int32_t rem = BinaryOperate(SpvOp::SpvOpSRem, a, b);
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int32_t b_prim = static_cast<int32_t>(b);
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return (rem + b_prim) % b_prim;
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if (b != 0u) {
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int32_t rem = BinaryOperate(SpvOp::SpvOpSRem, a, b);
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int32_t b_prim = static_cast<int32_t>(b);
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return (rem + b_prim) % b_prim;
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} else {
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// Mod with 0 is undefined, so we will just pick 0.
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return 0;
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}
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}
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case SpvOp::SpvOpUMod:
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assert(b != 0u);
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return (a % b);
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if (b != 0u) {
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return (a % b);
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} else {
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// Mod with 0 is undefined, so we will just pick 0.
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return 0;
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}
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// Shifting
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case SpvOp::SpvOpShiftRightLogical: {
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@ -434,6 +434,46 @@ INSTANTIATE_TEST_CASE_P(TestCase, IntegerInstructionFoldingTest,
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"%2 = OpBitwiseAnd %uint %load %uint_0\n" +
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"OpReturn\n" +
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"OpFunctionEnd",
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2, 0),
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// Test case 17: fold 1/0 (signed)
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InstructionFoldingCase<uint32_t>(
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Header() + "%main = OpFunction %void None %void_func\n" +
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"%main_lab = OpLabel\n" +
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"%2 = OpSDiv %int %int_1 %int_0\n" +
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"OpReturn\n" +
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"OpFunctionEnd",
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2, 0),
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// Test case 18: fold 1/0 (unsigned)
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InstructionFoldingCase<uint32_t>(
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Header() + "%main = OpFunction %void None %void_func\n" +
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"%main_lab = OpLabel\n" +
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"%2 = OpUDiv %uint %uint_1 %uint_0\n" +
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"OpReturn\n" +
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"OpFunctionEnd",
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2, 0),
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// Test case 19: fold OpSRem 1 0 (signed)
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InstructionFoldingCase<uint32_t>(
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Header() + "%main = OpFunction %void None %void_func\n" +
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"%main_lab = OpLabel\n" +
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"%2 = OpSRem %int %int_1 %int_0\n" +
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"OpReturn\n" +
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"OpFunctionEnd",
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2, 0),
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// Test case 20: fold 1%0 (signed)
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InstructionFoldingCase<uint32_t>(
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Header() + "%main = OpFunction %void None %void_func\n" +
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"%main_lab = OpLabel\n" +
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"%2 = OpSMod %int %int_1 %int_0\n" +
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"OpReturn\n" +
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"OpFunctionEnd",
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2, 0),
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// Test case 21: fold 1%0 (unsigned)
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InstructionFoldingCase<uint32_t>(
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Header() + "%main = OpFunction %void None %void_func\n" +
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"%main_lab = OpLabel\n" +
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"%2 = OpUMod %uint %uint_1 %uint_0\n" +
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"OpReturn\n" +
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"OpFunctionEnd",
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2, 0)
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));
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// clang-format on
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