On targets smaller than 64 bits, emit a compile-time error if withUnsafeTemporaryAllocation(of:capacity:) byte count overflows

Author: grynspan

lib/IRGen/IRGenSIL.cpp

@@ -3026,6 +3026,14 @@ static llvm::Value *getStackAllocationSize(IRGenSILFunction &IGF,
     auto overflow = llvm::MulOverflow(*capacityValue, *strideValue, byteCount);
     if (overflow) {
       Diags.diagnose(loc, diag::temporary_allocation_size_overflow);
+    } else {
+      // For architectures narrower than 64 bits, check if the byte count fits
+      // in a (signed) size value.
+      auto maxByteCount = llvm::APInt::getSignedMaxValue(
+        IGF.IGM.SizeTy->getBitWidth()).getSExtValue();
+      if (byteCount > maxByteCount) {
+        Diags.diagnose(loc, diag::temporary_allocation_size_overflow);
+      }
     }
     result = llvm::ConstantInt::get(IGF.IGM.SizeTy, byteCount);
 

test/IRGen/temporary_allocation/bad_constants.swift renamed to test/IRGen/temporary_allocation/size_too_large.swift

@@ -3,7 +3,7 @@
 @_silgen_name("blackHole")
 func blackHole(_ value: UnsafeMutableRawPointer?) -> Void
 
-withUnsafeTemporaryAllocation(byteCount: 1, alignment: -1) { buffer in
+withUnsafeTemporaryAllocation(of: Int.self, capacity: .max) { buffer in
     blackHole(buffer.baseAddress)
 }
-// CHECK: error: alignment value must be greater than zero
+// CHECK: error: allocation byte count too large