[clang] [clang] Implement __builtin_stdc_rotate_left, __builtin_stdc_rotate_right (PR #160259)

[Eli Friedman via cfe-commits]

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@@ -15774,7 +15768,53 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
         !EvaluateInteger(E->getArg(1), Amt, Info))
       return false;
 
-    return Success(Val.rotr(Amt), E);
+    // Normalize shift amount to [0, BitWidth) range to match runtime behavior
+    unsigned BitWidth = Val.getBitWidth();
+    unsigned AmtBitWidth = Amt.getBitWidth();
+    if (BitWidth == 1) {
+      // Rotating a 1-bit value is always a no-op
+      Amt = APSInt(APInt(AmtBitWidth, 0), Amt.isUnsigned());
+    } else {
+      // Divisor is always unsigned to avoid misinterpreting BitWidth as
+      // negative in small bit widths (e.g., BitWidth=2 would be -2 if signed).
+      APSInt Divisor;
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efriedma-quic wrote:

You can declare Divisor as an APInt; every use coerces from APSInt to APInt anyway.

https://github.com/llvm/llvm-project/pull/160259