Print warning when operator<< shifting too much (#4255)

* Print warning when operator<< shifting too much

Closes #3944

For the given type of the left side operand to `operator<<` is not big
enough for the right side operand, print a warning that the result will
be always zero.

1 files changed, 70 insertions, 0 deletions

diff --git a/source/slang/slang-ir-operator-shift-overflow.cpp b/source/slang/slang-ir-operator-shift-overflow.cpp
new file mode 100644
index 000000000..33ee53262
--- /dev/null
+++ b/source/slang/slang-ir-operator-shift-overflow.cpp
@@ -0,0 +1,70 @@
+// slang-ir-operator-shift-overflow.cpp
+#include "slang-ir-operator-shift-overflow.h"
+
+#include "../../slang.h"
+#include "slang-ir.h"
+#include "slang-ir-insts.h"
+#include "slang-ir-layout.h"
+
+namespace Slang {
+
+    class DiagnosticSink;
+    struct IRModule;
+
+    void checkForOperatorShiftOverflowRecursive(
+        IRInst* inst,
+        CompilerOptionSet& optionSet,
+        DiagnosticSink* sink)
+    {
+        if (auto code = as<IRGlobalValueWithCode>(inst))
+        {
+            for (auto block : code->getBlocks())
+            {
+                for (auto opInst : block->getChildren())
+                {
+                    switch (opInst->getOp())
+                    {
+                    case kIROp_Lsh:
+                    {
+                        SLANG_ASSERT(opInst->getOperandCount() == 2);
+
+                        IRInst* rhs = opInst->getOperand(1);
+                        auto rhsLit = as<IRIntLit>(rhs);
+                        if (!rhsLit)
+                            continue;
+
+                        IRInst* lhs = opInst->getOperand(0);
+                        IRType* lhsType = lhs->getDataType();
+
+                        IRSizeAndAlignment sizeAlignment;
+                        if (SLANG_FAILED(getNaturalSizeAndAlignment(optionSet, lhsType, &sizeAlignment)))
+                            continue;
+
+                        IRIntegerValue shiftAmount = rhsLit->getValue();
+                        if (sizeAlignment.size * 8 <= shiftAmount)
+                        {
+                            sink->diagnose(opInst, Diagnostics::operatorShiftLeftOverflow, lhsType, shiftAmount);
+                        }
+                        break;
+                    }
+                    }
+                }
+            }
+        }
+
+        for (auto childInst : inst->getChildren())
+        {
+            checkForOperatorShiftOverflowRecursive(childInst, optionSet, sink);
+        }
+    }
+
+    void checkForOperatorShiftOverflow(
+        IRModule* module,
+        CompilerOptionSet& optionSet,
+        DiagnosticSink* sink)
+    {
+        // Look for `operator<<` instructions
+        checkForOperatorShiftOverflowRecursive(module->getModuleInst(), optionSet, sink);
+    }
+
+}